Like all spells that require targets, Squirming Emergence will check to make sure its target is still legal as it tries to resolve. Use the number of permanent cards in your graveyard at that time, even though it may be a different number than the number that were there as you cast the spell. If the permanent card's mana value is greater than the number of permanent cards in your graveyard at that time, Squirming Emergence won't resolve.