Leaving a sugar water feeder up in autumn will not keep Ruby-throated Hummingbirds from migrating. Hummer migration is stimulated by photoperiod, so as days become shorter in fall local hummingbirds begin to put on fat and soon depart for the tropics. Nearly all hummers that stay behind are those that are ill or "genetically inferior," and it's likely they would die in migration anyway.
At most locations in the eastern U.S. and southern Canada, 99.9% of the ruby-throats are gone by 15 October, and adult males don't begin to return until mid-March. Females follow soon thereafter.
We suggest you maintain one half-full hummingbird feeder through the winter for as long as you wish, changing the artificial nectar weekly. You may need to bring the feeder in at night to keep it from freezing and put it out the next morning when you fill your seed feeders....
http://www.rubythroat.org/FeedersMain.html