When the hero deck runs out

[mqstout]

The expansion "toss hero cards" cards tend to get rid of greater numbers of them from what I recall.
Also, there is bonus to heroes having more cards in discard (for Pick Up: abilities).

Even playing just base game a bunch, no expansions, the hero deck was never in threat of going out.

To preserve this, one could utilize the rules from the one scenario where the heroes build a specific "town life" deck that zombies can attack. I forget which scenario that is.