Found this on the game’s official Facebook page:
Can I unlock Cleveland after the event ends?
If you have the museum built, you can still unlock Cleveland after the event ends, but it’ll be harder! Some of the items needed to unlock him will change. Once the event ends, the museum will automatically be moved to your inventory. Place this building back into your town to start collecting the new items needed.
What happens to the Adventure Peter or 80s Pop Star Cleveland costume?
If you have unlocked Adventure Peter or 80s Pop Star Cleveland, these costumes will stay in your game. If the costumes are still locked, they will no longer be available in the game after the event ends.
Can I still unlock King Butt?
If you collected enough moon idols to unlock King Butt, he is yours to keep raging in the game. If you did not unlock him, he will no longer be available when the event ends.
What happens to the moon idols?
Spend all your moon idols now! These golden booties will go away after the event ends and they will not convert to other forms of currency.
What happens to the pyramid?
When the event ends, the whole event district, including the pyramid, will go away.
What happens to my treasures?
Any unclaimed prizes from your Treasures tab will be moved to your inventory.
Just in case you hadn’t seen it! Keep butt grindin!