Chances of Moscow becoming part of Poland again?
Impossible. Times changed. Back in past, two factions of Slavdom/Sarmatia in wide sense (essentially it was Sarmats vs. Scythians) clashed for Moscow. Today, Moscow represent distant cousin but, important point of balance for Poland.
If Russia collapse, Anglo-Germanics and Chinese would grab everything. Plus, Germanics would take Poland, on the top of all, like the strawberry on the cake. Just to prove the point, which state that all Slavs must extinct.