I don't think Marriott would comp you just because you were Starwood Platinum, but you might be able to requalify by meeting a short-term goal? Several years ago, I was not able to maintain black level, but they gave me an offer to stay X times during the next 3 months to maintain. I believe it was approximately 1/4 of the annual goal.

I would offer something rather than simply asking them to comp you the level.