hi. Would appreciate any substantiated feedback on this question:

I am flying on a Delta Amex Plat companion ticket in a few weeks from SEA-ROA, returning ROA-DTW-SEA.

It turns out that I need to be in CVG for a meeting that starts the next morning.

Ideally: I buy ticket DTW-CVG; CVG-SEA on Delta, travel the ROA-DTW of my companion reservation then split off from my companion (who is Gold) who has to continue on to SEA. Per the Diamond desk, if I do not take the DTW-SEA leg, they will detect it at that time and not let companion fly.

Alternative: I fly all the way back to SEA, and turn around on a redeye on a diff airline, which is cheaper and thus what my travel policy requires (also nervous doing this in case DL flight is delayed)

Alternative 2: I fly all the way back to SEA, pay the extra amt to fly Delta, and get right back on the redeye back to DTW, then onto CVG 2 hrs late for the start of my meeting

1) Will they really deny my companion travelling the DTW-SEA leg if I'm not on board that flt?
2) Assuming my companion is able to fly, can they charge some sort of penalty after the fact?
NOTE: our PNRs are split if that makes a difference.

thanks in advance!