Rematch clause usually is only for the champ in case he lose. Wlad have no belts so I can't see him having a rematch clause. I could be wrong though. The better question is does Joshua have a rematch clause since he is the champ.
Win or lose, this will be Wlad's last fight. If he wins: he gets his belts back and doesn't end his career on that loss to Fury and retires as a champion, if he loses: he will know his time has passed.
Wlad is going to retire. He is doing everyone a solid at this point by being the sacrificial torch bearer and passing it to Josh. Fury could have been the one, but the money has corrupted him.
I'd assume Wlad would stipulate a rematch clause as a must during any negotiations. He's experienced enough and lost enough times unexpectedly for it to be a prudent request for any fight he has. I'd expect the same from Joshua as well to be fair.