I doubt UA would follow through considering it is illegal to submit known false debts. Plus they're outright wrong that it constitutes "fraud," if for no other reason than the person skipping additional legs didn't profit from it, instead they simply limited UA's ability to further profit off of their travel. If this was "fraud" then any other airline discount or saving would be too. Shop around for the cheapest pric…
How about selling a ticket and then telling me I can't get on the flight because it's overbooked. Is that fraud too?
No, because overbooking is disclosed in the Contract of Carriage. See https://www.united.com/ual/en/us/fly/contract-of-carriage.ht..., section 5G.