Question of ending the game in Cthulhu

[Moto321]

Imagine there are 3 players in game. 2 of them are already Cultist. The non-cultist player uses a Cultist Class card in their turn, having the highest level, so they become a Cultist and the game should end.

I know O R'lyeh? can be used to deflect the Cultist Class card and the game does not end, but my question is: after activating the Cultist Class card, can the other players use as many as Level-Up cards they have in hand, or does the game end immediately?

Thanks in advance.