Rip, Spawn Hunter

If a creature's survival ability triggers but the creature leaves the battlefield before the ability resolves, use its tapped or untapped status as it last existed on the battlefield to determine whether or not the ability will do anything.

The value of X is determined only once, as Rip's ability resolves.

If a creature with a survival ability isn't tapped when your second main phase begins, the ability won't trigger at all. You won't be able to tap it during your second main phase in time to have that ability trigger.