They'll only charge your card if:
1. It's your checkout day (or actually, the early evening of the night before)
2. You're approaching your resort credit limit
To avoid this, just go to the front desk before your checkout day or before you reach your credit limit (whichever comes first) and tell them you'd like to apply your balance to GC(s). They'll happily do this. If you've combined multiple cards onto one, it'll make the process much quicker, as the CM will only have to apply one card to the balance. If by chance they've already charged your card, they'll be able to reverse the charge so you can use your GC(s).