I'm in a similar situation, only it's my main character.

You could pull the classic "It looked like I died but not really" and play with misinformation so that there's doubt that the death occurred. That gives you a chance to bring the character back if you want.

You could also explore taking him near death but not really killing him. I suspect the reactions would be the same and it would provide a growth opportunity for your other characters.

Putting him into a profound coma from which he is never expected to revive might give you the same options. He could die later or he could recover.