If one fell asleep before the Friday night meal and didn’t wake up until the next morning, must he eat three meals on Saturday?
If one didn’t eat the meal on Shabbos eve, he should eat three meals the next day. The first meal is considered like the Friday night meal, the second like the Shabbos day meal, etc.
There is however one difference. The poskim say that if he forgot to say ritzay during the second meal of the day, (which would usually be shalos seudos, that he doesn’t have to bentch again), that he doesn’t have to bentch again similar to forgetting ritzay by shalos seudos.
Rema O:CH 291-1, M:B 291-6.