jen, my best guess is your original queen, or the queen that you found outside the hive is in that hive, and the bees or she, took care of the virgin queen you found dead outside the hive. when you inspect the hive, look for her, and also look for other young queens.
to your question, any queen will not be able to mate this time of year (lack of drones) and also late summer/ fall supersedures are not going to be good queens. (how they are fed + drone population).
"is it possible for this new queen to wait until spring to mate for next years production?"
what iddee said, no.
what should you do? not knowing what's been going on in there in the past month, and what's going on now with the recent developments?
personally with the 'problems' you have experienced with this hive, i would be inclined to send the queen off on a farewell, cut every cell, (if they exist) and any other queen, (if they exist) leave them queenless for a day (make sure they are queenless) and combine it with another hive, and distribute the resources. in the spring you could potentially make some nice divides. also, your problem with that deep is solved. how strong is this colony? if the bees are trying to replace the queen, this is a clue. also consider that this hive may not make it with the existing queen. you don't need a hail mary hive. also, i would not purchase a mated queen.