It is generally not done, but there have been instances of this happening. Anyone returning would come back at the bottom of the seniority list. The chief pilot was a former line pilot who left at one point and was re-hired last year into his current position. We also have another DCA pilot who left years ago and spent a long time captaining DC-8s, but he never left voluntarily as he had been furloughed and simply never returned. But he was re-hired about 8 or 9 years ago and kept his old employee number, but not his previous seniority.

So it is not unprecedented, but it is generally not done. But it could happen if the candidate in question had previously been successful and left on good terms I suppose.