21K pilots. That sounds like the approximate number of regional pilots. If regional airlines disappeared, bringing all of that flying back to mainline, would anyone be upset?

IF a shortage did materialize (that's a big if), there would probably be a few regionals, LCCs, and ULCCs that went out of business due to them not being able to hire pilots at food stamp wages. I don't see a problem here.

Majors that pay good wages won't have problems recruiting pilots. Airlines that can't compete with living wages will go out of business. It sounds like Sun Country (I thought they went out of business years ago) may close its doors because management says that they can't pay their pilots higher wages. Sun Country Airlines owner warns of possible shutdown | Duluth News Tribune
After looking at their pay scales, Sun Country needs to be shut down. And every single pilot there could find a higher paying job somewhere else.