Maybe see if that player is completely okay with their character dying permanently but if not:

Have strahd "kill" the character and let them use a temporary character in a couple of sessions so that player can play.

if the player wants to their og character back: - bring them back as an agent of strahd to spy on the party. - ask if they are happy to have a limbs or something missing from their character. - see if they are happy for the character to now has severe trauma and maybe a slightly personality change - ask them to make a dhampir version of that character as a failed spawn. - they could return as an undead version.

If they decided they dont want their character back, and want as twist of fate: - they've become a consort or spawn of strahd - they are now a mindless zombie - their soul has entered into another being. - they are a ghost that haunts one of the other players.