Piedmont(original) went under when USAir won the war of bids against Norfolk Southern(who would have kept them flying as Piedmont). At that time Piedmont was looking to purchase TWA with Norfolk Southern's large cash reserves; which I'm sure would have been a better deal than what they got in the AA takeover. USAir; seeing the writing on the wall of competing against a much larger and better competator that the combined Piedmont and TWA would be, offered a bid to purchase Piedmont; even though it's aquisition of San Diego based Pacific Southwest Airlines wasn't even complete. Carl Ichon got involved to help Piedmont(he wanted to offload TWA to Piedmont) buy announcing that TWA wanted to aquire USAir. His bid got rejected by the DOT, so Norfolk Southern didn't have that ammo to block USAir's bid and didn't want to raise the bid, so Piedmont's board which was backed in a corner, took USAir's bid.
The current Piedmont was actually Henson Airlines. When they rebranded USAir as USairways the renamed all the wholly owned commuter carriers. Jetstream became PSA, Henson became Piedmont, Allegheny kept their name, and CCAir was sold off to MAG.
Both Piedmont and Pacific Southwest Airlines (originals) had very loyal employees and both had very unique corporate cultures that were decimated by USAir and it's managment vs. employees style of corporate culture.