2 ideas:
1- Old lich that steal the holy xp from the players, putting them back at level 1 with the big total of 0 xp. Normaly when this lich do this, it put the character into the very eldery age range; but this time it isn't givin the player a change to come back (and a new magical tatoo that is the result of the operation that have some side effect like can't be spyed by magic, must try to steal holy symbol that are into a temple of good god but have nothing to do with the holy symbole after stealing them, add a pinch to all the king picture they see....let them rool will save to avoid doing thing but put a high number). The lieutenant of the lich are using the old equipement of the players again them.... A good way to make a compagn to last longuer (level 16 back to 1 then to level 18). Never say to a DM I love this group and everyone is sad because we are going to get near of the max level and stop playing them.
2-do adventurers pay tax in your world, if yes a corrupted tax collector that have taken their gold (with some extra because the players didn't have followed the normal procedure), and never given it to the king. Do that for a few level until a uncorupted tax collector come to the party and ask them for the money they own. Then this new tax collector inform the party that they can pay their tax by getting the corrupted tax collector in prison (but the corrupted one have run off in a far place). Do they where the only ones conned (probably not) and what they will do with all the money in the corrupted one hands after they get him? warning paladins can lose they pladinhood if they keep all the money for them-self).
In general, I have found that if the players recall the vilain name. Then this vilain was a good one. And interacting with him a few times help a lot to do that. Just don't force the interation to much or they may begin to hate the DM not the vilain.
