Without so many roads across Long Island, perhaps the suburban development would be slowed down. Less housing means less support industry. Less support industry means that Long Island's proper industries could remain here, at least for a while. Grumman and Republic could still be here.
More plausibly, the NYC subways wouldn't see so much decay. With more focus on rapid transit, the 2nd Avenue line or even the LIRR-Grand Central connection could be done by now. If only...
Without the Staten Island-Brooklyn connection of the Verrazano Bridge, we may finally see a rail tunnel between Staten Island and Manhatten.