I think you should still be able to collect tax, I guess substitute the money with come other tokens from some other game until you can get the "real" ones back in the play. I think it would be too harsh not being able to get coins just because other players are not spending them.
The bank ran out of money because my son got a bunch of knights, and a building that gave coins for knights, and kept taxing an extremely large grass field, AND had the Queen, AND didn’t spend more than 1 coin on buildings. So each tax gave him double digit coins, and he was hoarding them for end game points. He ended up with 50 points in coins alone. His grass field was 144 points.