Not that surprising or "ballsy" by the author, really.
Claude was getting increasingly unhinged and violent to the point where you wondered why he hadn't been arrested already with all the shit he pulled. All that was needed was for the author to write a reason for him to go all the way over the edge.
The other two of the Foul Four got their Mandatory Moment of Redemption, and became cannon fodder the moment they had it.
And Dorothy announcing she was going to dump him like some old trash and not expecting some kind of retaliation in the state of mind Claude was obviously in? No sense of self-preservation whatshowever...
We'll see Claude back. Only question is how he will be "enhanced" to "drive the Plot". Underground drug, Demon Pill, demonic contract, Evil God? So many options...