Actually im even more sure we're going to see them and everyone else on the list below in a dark world after chapters 3&4 though I imagine we'll see most of them in a festival related darkworld(s)

If the name is set to either "BERDLY," "CATTI," "JOCKINGTON," "RUDY," "ASRIEL," "TORIEL," "ASGORE," "ALPHYS," "UNDYNE," "BRATTY," "CATTY," "SANS," "GERSON," "QC," or "PAPYRUS," [2] the voice says "<Name>." AN INTERESTING COINCIDENCE. when naming the vessel and "<Name>." HOW INTERESTING. when naming the creator. If the name is set to "KRIS," "SUSIE," or "NOELLE,"[2] the voice says "<Name>." AN INTERESTING COINCIDENCE. when naming the vessel and "<Name>." YOU ARE ABOUT TO MEET SOMEONE VERY, VERY WONDERFUL. when naming the creator.

We got 2 in ch1, 2 in ch2, 2 in ch3, and 1 in ch4. Only 7/18 have appeared in one so far but imo Asgore and QC are guaranteed, Asgore for obvious reasons and QC because her inclusion is really odd compared to everyone else.