I think you've received lots of great advice here already. One additional thing you may want to keep in mind as you're weighing your options is how the manner in which this character exits may impact other players.

Obviously, the needs of this player come first, and making whatever changes they need to ensure they can keep having fun in the game is most important. But I bring it up because, in a similar situation where I was running a game for a player who wanted to switch characters, I executed the change in a bit of a clumsy way that one of my other players found frustrating.

I had worked together with the player who wanted to change to craft a heroic last stand scenario in which their old character would sacrifice himself to allow the rest of the party to escape. Critically, we didn't discuss these intentions with anyone else at the table. One of my other players picked up on what was happening the moment we started playing it out, and did everything he could to prevent the loss of a party member. I essentially railroaded right over anything they tried.

Afterwards, they told me that while they understood why I ran it that way once the other player had a chance to explain their intentions and new character, it still wasn't very much fun to play through in the moment.

All this to say, if I had to do it again, I would make sure I have some sort of buy-in from the other players. They wouldn't need to know all the details, certainly, but I think a little heads-up would have made that experience much smoother for everyone.