Thanks, I'm glad you enjoyed the game.
I did not even think about it when making this game but someone rightfully mentioned that in practice the expansion of the mecahnics in bigger games is in fact when your party is separated in several groups in some parts of a dungeon, as a party whose size decreases as the game goes might be a bit unsatisfying outside of the context of this small game meant to implement a given theme.
But now what you describe with characters fusioning into alternative classes (but without being replaced by new ones unlike what's done with games I can think of with fusioning, or maybe still with replacement?) might also be some very cool system for a last part of a game for example, especially if I stop making boring, gritty, down-to earth games where you end the story retiring with some money and start making engaging, epic ones when you end up as gods fighting other gods instead.