When the hero deck runs out

[StayPuft]

I've always kept everything for Timber Peak separate. Beyond that, over time I collected ALL of the expansions. For the original game, I just mixed all the cards from expansions in and used the full deck.

To be perfectly honest, my group and I were perfectly fine with that for two reasons. One, even with just the base game deck for a while there, we never even came close to having the game end that way.

Two, to be perfectly honest, that's always felt to us like kind of a lame/boring/anticlimactic way for the game to end anyway. So, we don't mind that much making it so less likely to happen.

But, there certainly are ways around it if you prefer leaving the option there, as others have suggested.