Some have a custom to read Shir Ha-shirim (the Song of Songs) upon completing the Hagada, as it alludes to the love between God and Israel.
Though we have fulfilled our obligation to tell the story of the Exodus by reading the Hagada, there is a mitzva to continue embellishing the story and telling of the miracles and wonders that God did for our ancestors throughout the night of the fifteenth, until one is overcome with sleep. This mitzva includes studying the laws of Pesaĥ (SA 481:2; Gevurot Hashem ch. 2), but it does not include “pilpul” (talmudic casuistry) (Derashot Ĥatam Sofer p. 265).
It is best not to spend a lot of time on the portion of the Hagada that precedes the meal, because we want the children and all of the participants to remain alert until the fourth cup. But after finishing the Hagada, there is a mitzva to continue discussing the Exodus as much as possible.
If one fears that by staying up late he will be unable to pray Shaĥarit properly, it is better that he goes to bed earlier (Sidur Yaavetz). An effort should nonetheless be made to continue relating the story of the Exodus until after midnight (Kaf Ha-ĥayim 481:11).
Before going to sleep on Pesaĥ night, it is customary to recite Shema and the berakha of Ha-mapil, but not to read the other verses that are read on all other nights. These verses are recited as a protective remedy against harmful forces, but this night is safeguarded against such forces and opportune for redemption (Rema 481:2; and see Ben Ish Ĥai, Tzav 38).
May it be God’s will that just as we have merited to study the halakhot of the Seder, so may we merit to fulfill them.