I wonder what happens if you don't kill Louey

[Müşkülpesent Simyacı]

I'm so sad for killing louey. I want to know if you don't kill Louey, what happens?

[Pixus]

The game probably keeps going on, seeing as you have to kill Louey to progress.

[fafner2000]

I tried not to kill Louey, I really tried not to. But he kept hanging right before my eyes doing nothing, as if begging for me to end his sufferings. So I finally granted him his wish. So no, you probably can't go on without killing him.

[Janosch]

Nice

[Solitaire]

So, in the end of ACT 3, you ARE forced to kill him to progress, but he's not really dead :

In the Finale, you can spare him by just waiting when he's here, especially if he doesen't have his glitchflies up,it avoids having the "alas you truly deserve it" text, just like you aren't forced to kill lucifer if you don't hit him that much.It wont change the ending doe, he'll still look undead in the ACT 3 continuation