It looks like they could have survived. A group of scientists were trying to identify flood-prone areas in the region and assess the potential impacts of sea level rise by running a series of simulations, and they discovered that if the inmates had left after 11:30pm, they had a near 100% chance of survival.

https://www.sciencenews.org/article/alcatraz-escapees-could-have-made-it-safely-shore