I think in the OP's case the passenger staying on the original flight will have already benefitted from the elite's bag allowance, etc. so that if the PNR is split, it shouldn't matter. I can't imagine the GA telling the passenger to move out of elite or exit row seats right before closing the door when the OP's no show becomes apparent.

Am I missing something here? The PNR will be split automatically at T-10 minutes before the original flight but so what.