Maybe level 30 is the level where you achieve your epic destiny, meaning that you don't need to play after that. A new god is born or you finally reach Nirvana or something in that vein.
If I would have a campaign ending at that level, I would start a new campaign at level 1 but with the campaign world changed. A new level 1 cleric that is the servant of a PC that reached level 30 in the last campaign. Something like that.
