Totally get that and I feel bad for the pax that was given the se
At and then had it taken away. IMHO, DL is being irresponsible when they do this. I have also been in the situation where they gave my seat away and then refused to reinstate it. That never goes well for the GA.

Your point speaks to the fact that DL should stop this practice. It would be Better to let you take your seat in Y and then move you to F just prior to shutting the door if the other pax fails to make it. Then there's no harm, no fowl.

I hope the profusely apologized to you and offered something for service recovery.