I am most definitely NOT one of the pros on here; but "the dam had partially washed out" tells me that water has run over the dam which tells me other fish could swim in. I had purchased a pond of about that size with seemingly only a few smaller bass in it. Puzzled us until the 14 pound channel cat was caught. We then drained, rotenoed and only had a very few more small bass float up. You may already have a big predator in there.
If they have money to shock, they can probably can get money to drain, rotenoe, repair dam putting pipe in overflow) and restock with forage instead. I doubt it would cost that much if you check around.
Several years of grass shrimp, scuds and fatheads reproducing without other predators could result in a great forage base when the time comes to stock.