[Truth29]

"Do they really expect to get their money back? What concession could Russia take advantage of?"

Basing rights for ships? Access to their old missile bases? Lots of possibilities.

[NorseViking]

Missile base is a safe bet. Cancelation of IRBM treaty disproportionately benefits US at this point. US has multiple places to put IRBMs to target Russia and Russia lacks any within intermediate range from mainland US. Returning to Cuba is a perfectly logical idea from their perspective in that sense.