I believe there are some trained/imprinted [Lesser?] flamingos being used in a free-flying demo some where. As for actually trying to hold them in a free-flying living situation, I don't think it has been done. I believe the usual scenario is unpinioned wing-clipped flamingo moults out cut primaries, grows new ones, flies away. Home-bred birds do the same as soon as they can fly. The famouse Hialeah racetrack flock of Caribbeans started off as a pinioned flock, and I believe they started leaving the young full-winged. Eventually, as I understand it, the whole lot [minus any original pinioned birds] took themselves back to the Caribbean.
In the bad old importing days, occasional flamingos that had flown away from collections lived wild in the UK, often for several years. I remeber seeing three together on the Chesil Fleet [saltwater coastal lagoon in Dorset famous for the Abbotsbury Swannery] back in the 70s. One of these [Chilean I think] got too close to a nesting swan and was killed, and a single Caribbean [well enough known to be called 'Dilly' by the swanherd] used to commute between Abbotsbury and Poole Park [some 35 miles away] over many years before disappearing. Don't know what happened to the third bird. In the past few years a single Chilean has flown into the swannery, and was eventually re-homed at Slimbridge.