The return part of Fairground warden doesn't actually use the stack: The death of Fairgrounds Warden marks the end of the ability's duration. Just like there's no use of the stack when an "until end of turn" effect ends. This is actually a "fixed" version of older cards that had two separate abilities, like oblivion ring where the return ability would go onto the stack.
As for being hit by the boardwipe: The creature was gone while that warden was alive, so it will be safe. (It can't come back until the warden dies, and if the warden dies to the spell in question, it must still have been on the field)
I have one of his creatures exilied under my Fairgrounds Warden.
I play Wrath of God(or something similar i cant remember...) blowing up the board.
Now the question. Where on the stack is the creature exiled under Fairgrounds Warden returned?
and would it have been hit by the boardwipe?
UBRJeleva, Nephalias Scourge: ...and the storm arrivedRBU
BGHapatra, Vizier of PoisonsGB
WAvacyn, Angel of Hope: Avy, Baby!W
As for being hit by the boardwipe: The creature was gone while that warden was alive, so it will be safe. (It can't come back until the warden dies, and if the warden dies to the spell in question, it must still have been on the field)
UBRJeleva, Nephalias Scourge: ...and the storm arrivedRBU
BGHapatra, Vizier of PoisonsGB
WAvacyn, Angel of Hope: Avy, Baby!W