Interesting bit of data: Tonight my Hero rooms for one challenge regenerated, but they did not for another.
In Sharpstone, I had exhausted my Hero rooms; I’ve been playing that one for the past few days and had no new hero rooms. Tonight, however, I go in and got 2 fresh Hero rooms; both were under the room #25 mark (13 and 15 I think).
I then went into Harvestfield and observed that the same Hero rooms that I’ve been unable to open for a while now are still there, in the exact same place, with the exact same hero/lv requirement.
I didn’t check the Mines yet, but I suspect and hope that when I do, i’ll find some fresh Hero rooms waiting for me.
Once a week (Saturday night at 9:00 PM ADT, same time as the store deals regenerate), challenges where at least one Hero room has been exhausted will have 2 fresh Hero rooms placed in them; unopened Hero rooms are lost.
I say “at least one” because it’s quite possible that a player has been able to open one room, but not another, and will not be able to open the 2nd for a while. They also might not be strong enough to even reach a 2nd Hero room; in Sharpstone, I’m only strong enough to make it up to room 25. Replacing this 2nd one thus makes sense to let the player eventually have rooms that they will be able to open.
Oh, and I say 2 Hero rooms because I don’t think I’ve seen more than 2 in a challenge. I could be wrong though, having merely not been able to reach a 3rd.