Here's a way to handle it that should be really fun for the eliminated player and will make him a good threat for everyone else.
If the scoring is point based, instead of receiving points for his new role, the recincarnated character could cost the other players points (same as receving but more fun) if he evenly destroys others' stuff. For example, in a 4-player game, after Player A is eliminated, if he can destroy one unit of Player B, one of Player C, and one of Player D, they all lose a point. That is, for each set of the other players' stuff destroyed, they lose a point
Then at end game, for each unbalanced subset above one, that player loses a point. So if at end game, after removing all of the full sets that the player scored for, if the player had destroyed an additional BBBCC, he'd lose two points (one B and one C is fine, then an extra BC is one point lost, and an extra B is one more point lost).
(Note that if any other player is eliminated, his player-monster already-destroyed tokens would still count towards completed and uncompleted sets -- you can't wipe someone out in order to not have their extra tokens count against you.)
This encourages him to go on a rampage, wiping out everyone, but wiping out everyone as evenly as possible. He still improves his position, but only if he hurts everyone else.
That way you wouldn't have to worry about territory or monster speed or anything else. Yes, he could still end up playing kingmaker, but only at the direct expense of hurting his own score, something that players don't usually do as it's considered poor gamesmanship.
Yep, I definately get what you mean ;)
It would give the defeated player a good position to play, it would be fun, and they would be against Everyone, not just the player who eliminated them. You could also work in some way that gives players more of an incentive to try and totally wipe an enemy out - if I knew that when I took a player out, they would come back as a rampaging horde, on the other side of the board to myself, and that they would start attacking my enemies, then it would give me a greater incentive to go all out and try and really beat someone down...
I must sound like a really evil gamer don't I! Its not that I am always overly aggresive, I just like the option to be so sometimes ;)
The game's theme could easily be developed with these types of mechanics in mind. There could also be time-based incentive to be the first to eliminate someone else, for example if there was not some mighty sacrifice (wiping out an entire empire...) by a certain turn than ALL the undead hordes (somehow game controlled) in the game would rise up against all the players... However if a player was eliminated, then only one horde would arise, and would be controlled by that eliminated player...
Could get very nasty very quickly, and end up in players ganging up against others. There could also be ways to determine where the eliminated player would restart. Starts to have a similar kindof feel of player roles as 'Betrayal at House on the Hill' where one player turns against the rest, but in this case, the players get a chance to 'choose' who this player is, by killing them off!