But most are seasonal and it really depends on the general climatic change of temps as to when the "seasonal" ones close.  I'd suspect most of the seasonal ones would be closed by mid - late October.    

But hey, there's always the option of private heated pools.

I stayed at the Wynn last December and the main pool was open. I heard that the pool was heated but figured it was a wives tale. Because it was 40 degrees outside i was wearing a winter coat and long pants. I saw people peeling off their clothes and jumping in with swim suits. There was pool side servers wearing sweat suits serving food and drink. There were also lifeguards wearing sweats. No one appeared to be cold and looked like they were having fun.