One thing I learned from consulting is if you position yourself as the "fix your mess" guy you have to be very defensive. Ask for more up-front, and bail at the first sign of underpayment. Be pleasantly surprised when a poorly run project is being run by nice, honest people. Prep for the opposite.
But let's assume he got 100% upfront.
More importantly, he didn't protect scope or contract change requests. That was the time to contract. It sounds like collecting 100% would've been leaving money on the table for value delivered.
I like your label for "fix your mess" guys, but I know/use a few who definitely bill and get paid much later (especially lawyers). Sucks for OP that he contracted with a CN firm with credit risk.