Well they aren't really subsidiaries just partners in a marketing arrangement. So a death of UAL would not neccesarily take the others down as USAirways would most likely also kill PSA, Piedmont, and Allegheny since they are subsidiaries. But getting back to your question, frankly there is no way of knowing. Looking at history it wouldn't be good. History shows that when the mainline carrier goes so do the affiliates. For example, when Eastern shut down most of the Eastern Express companies went away about two weeks later. In all fairness they only operated as Eastern Express (although some did Continental Express at the same time) whereas most of the United Express carriers have other partners to fall back on. So I think at the very least their operations would be cut in half. Some speculate SkyWest may go at it alone in DEN
though. Who knows???? Let's hope we don't have to find out.