If a resident of Eretz Yisrael leaves for an extended period of time but still plans to return to Eretz Yisrael, his status is very unclear. On one hand, since he intends to return, it would seem that his status remains that of a resident of Eretz Yisrael. On the other hand, when the Sages spoke of one who intends to return, they may have had in mind one intending to return relatively soon. If so, it is possible that one who will be abroad for an extended amount of time is considered a resident of the Diaspora. Additionally, he might well decide to remain abroad.
There are two primary positions regarding this case. Some say that if a person leaving Eretz Yisrael plans to stay abroad for a year or more, he is considered a resident of the Diaspora, and he must keep two days of Yom Tov. This is the ruling of many rabbis in the Diaspora.
Others maintain that even if he intends to remain in the Diaspora for a number of years, as long as he is absolutely determined to return, he is only a temporary resident abroad, and his status remains that of a resident of Eretz Yisrael. Nevertheless, it is clear there must be some time limit, as it is inconceivable that one who intends to remain in the Diaspora for years and years continues to follow the practices of those who live in Eretz Yisrael. Therefore, it would seem that if he is planning to return within four years, he is considered a temporary resident abroad, as the longest sheliḥut (a temporary “mission” to the Diaspora, such as for the Jewish Agency, Israel’s Ministry of Foreign Affairs, and countless other companies and organizations) can last almost four years. However, one who intends to live abroad for four years or more, even if he definitely plans to return to Eretz Yisrael, must observe Yom Tov Sheni while he is abroad.
In practice, it is apparent that if one leaves Eretz Yisrael for a purpose that does not have a specific time frame, he should follow the first position. Even if he clearly intends to return to Eretz Yisrael, as long as he will be abroad for at least a year, his status while he is there is that of a resident of the Diaspora. This is assuming that his family moves with him; if his family remains in Eretz Yisrael, though, he retains the status of a resident of Eretz Yisrael.
In contrast, one who leaves Eretz Yisrael with a clear plan and a specific time frame should follow the second position. Therefore, if one goes abroad on sheliḥut, to complete a specific course of study, or for any other well-defined reason, he is considered a resident of Eretz Yisrael as long as he intends to return within four years. If he intends to stay for four years or longer, he should observe Yom Tov Sheni. Of course, there are many in between situations, and in such cases, a rabbi should be consulted with the specifics, and asked for a ruling.
What if a person is living in a Diaspora community that has one accepted rabbinic leader (mara de’atra) who is an outstanding halakhic authority? If that rabbi rules in accordance with the first position, then anyone living in his community must follow his ruling.
The first position is that a year is the determining amount of time. We know from elsewhere that after a year, a person is considered a local resident when it comes to paying taxes (Bava Batra 7b). Therefore, even though he intends to return, once he has left for a year he is considered a resident of his new location. This is the position of Avnei Nezer, OḤ 424:28; AHS 496:5; Tzitz Eliezer 9:30; and Ḥazon Ovadia, Yom Tov, p. 121. Many poskim who live abroad are inclined to rule this way.
The poskim who adopt the second position do not specify a number of years, but it is clear in context that they mean two or three years, or a bit longer. The rationale is that if one definitely intends to leave a place, only after a stay of a number of years is he considered a local. Mishneh Halakhot 4:83 states something along these lines, and this is also the opinion of R. Elyashiv (as cited in Yom Tov Sheni Ke-hilkhato, p. 162) and Or Le-Tziyon 3:23:5. Igrot Moshe, OḤ 3:74 takes this position regarding people who spend a year or two in Israel.
Many Diaspora rabbis follow the first position. (According to Ḥakham Tzvi §167, it would seem that even one intending to return to Israel must keep two days in the Diaspora.) Nevertheless, I wrote above that in practice, those who are going for a very specific purpose may follow the second position. This is because the basis of the obligation of the second day is rabbinic, and the principle is that we are lenient in cases of doubt about a rabbinic rule. Additionally, the second position seems to make the most sense.
Therefore, if a person leaves Eretz Yisrael without a well-defined goal, even though he intends to return, there is a certain chance that he will decide to remain abroad. Therefore, if he went for a year (or more), he has the status of one who lives abroad, in accordance with the first position. But if he has a well-defined goal with a specific time frame such as sheliḥut (whether in Jewish education or business) or studying for a degree, then even if he is abroad for a few years, his time there is still temporary, both in his own eyes and in the eyes of the community to which he currently belongs. However, there must be a time limit. Since people leaving with specific goals – whether for education or business – normally do not stay abroad longer than four years, that is the dividing line. People also perceive that someone who has been in a place for four years cannot claim that he is not a local.
If one leaves Eretz Yisrael for two years with a specific purpose in mind, and later decides to remain an additional two years, he should behave as a Diaspora resident starting from the time of his decision. Since he intends to live abroad for four full years, as long as he is abroad his status is that of a Diaspora resident, even if he visits Israel once or twice a year. However, during his visits, his status is that of a resident of Eretz Yisrael, since he has a deep connection to the land (based on Maharit Tzahalon §52, as cited in the next section).
An additional reason may be adduced in support of the opinion that a year is the decisive time period. It has become clear that when Israelis living long-term in a Diaspora community do not observe Yom Tov Sheni, they damage and weaken the locals’ relationship to holiday observance, and perhaps mitzva observance in general. In the past, one who lived abroad with his family for a year could no longer be considered to be a resident of Eretz Yisrael, as Radbaz pointed out. In general, the Sages said that even one visiting for one day may not deviate from local practice, out of concern for causing discord (Pesaḥim 50a; SA 496:3). We can broaden their logic and say that when a visitor intends to remain for a year, it is not sufficient that he behave externally like the community members. Since he becomes integrated into the community, the community members will certainly notice and be aware that he is not keeping the second day of Yom Tov. In order that he not undermine their practice, he has a responsibility to behave completely like them for all halakhic purposes. Along these lines, the Sages ordained a second day of Yom Tov for all the holidays, even when the messengers had already arrived, in order not to distinguish between holidays (RH 21a; see section 2 above). Similarly, they also ordained that berakhot be recited on the second day; if people were to eliminate the berakhot, the institution of Yom Tov Sheni would likely come to an end (Shabbat 23a; see section 5 above). Therefore, I wrote above that if a Diaspora community has an accepted rabbinic leader who is an outstanding halakhic authority, anyone living there must follow his ruling.