Hummingbirds don't stay because there's a feeder. When it's time to migrate, they will. That said, there are no guarantees that nature has this birds best interests in mind. Some birds do perish due to delayed migration but that may be natures way of weeding out insufficiencies.

If there are no blooms around, taking away this birds food source may deprive it of the important resources needed to attain the required physical state that will initiate migration. Maintaining a feeder is the best you can do to help this bird. It may have hatched very late and may just need one more day. You'll never know for sure.

Another thing to consider, is this bird a Ruby-throated? There are number of individuals of different western species that, for whatever reason, head east instead of south. Quite often, these birds are young birds so they all look very similar, green and white. Calliope and Rufous are probably the most common "lost" species but there are other possibilities.