If you read up on airline history, you'll find that getting the pilots with the planes is a big priority for ALPA. After they didn't place braniff pilots at eastern when eastern bought out the Latin American routes, ALPA realized the mistake in their ways and made it a priority since.
Obviously RAH are teamsters, but I think the United ALPA wouldn't throw all those pilots under the bus.

Also, the situation you're responding to (however unlikely) has never happened before. A major has not bought out any regional and absorbed its equipment, so to say that the pilots will all be SOL in this proposed scenario is not accurate. No one knows how that would turn out.