would it be possibly for nongodtiers (karkat terezi and kanaya ) to become godteirs after the game? i saw a headcanon once that roxy could be able to conjure up some quest slabs for them therefore letting them godtier is they die on it

Hard to tell, chances are they cannot quite ascend to God Tierhood in any normal way- However they don’t exactly NEED to. As we see with some, namely Terezi, and John pre-Ascension, non-God Tiers can still use their powers if they train them enough, and if they didn’t get immortality from the door, as some people headcanon, the Dave + Jane Fraymotif idea is still there, so it’s not like they’re in any hurry to go God Tier.