I understand that if you save Violet first or second nothing happens, and if you save her third or fourth you skip one or both intermissions. But what happens when you save her last? Does the game crash? Does the game not let you enter the final level so you're unable to beat it? Does something else happen, or does nothing happen at all?

The game softlocks because you are then unable to activate final level, at least until you start a new game.

that was a odd thing to ask

I tried saving violet last and the game didnt softlock, The cutscene after just shows 2 violets then you go into the final level

In version 2.3, rescuing Violet last was fixed to lead to the Final Level, instead of canceling the sequence (which would lead to an unwinnable save). The question was originally asked when version 2.2 was the latest version.

If you want, you can still softlock the game by pressing R after "Level Complete!" shows up and then touching a teleporter or saving and reloading your game.