I think it is rare that actual flight credit be given in lieu of being bumped or as part of a negotiated strategy. There have been posts in the past where FT'ers have been "promised" credit at the gate in a similar situation only to have the credit not post and argument ensue against the FFP authorities and a game of he said/she said.

Sure it's possible to get credit for a missing flight, but there's typically documentation (i.e. your BP and a record somewhere that you flew) that one actually flew. In the case of not actually flying, I don't know if a FFP will honor anything said at the gate.

I believe a search can yield some results regarding the scenario you described.

Good luck!