Sikorsky was a pioneering airplane designer before WWI and was well-known and greatly respected in Russia. Would he stay there after the revolution, he would probably be what Tupolev was IOTL. The Great Daddy of everything flying and having more than one motor. Sikorsky's IOTL forays into flying boats and choppers were mostly caused by necessity to find a relatively unoccupied market niche. Rigid Soviet system would keep him busy designing heavy planes and, most likely, would not allow him to dabble at anything else (although even that is not a given - after all, IOTL Tupolev worked, not too successfully, on naval aviation and even tried his hand, unsuccessfully, in heli design).
As far as helicopter is concerned, absence of Sikorsky would not change things a lot. His early design achievements were VERY closely matched by independent design teams in USSR, GB, Germany (Germans actually had industrially-produced helicopter in 1936). So, would he not develop the R4, somebody else would be christened "the father of helicopter", but that's about it.