I lost my android, and while it was lost I did the factory reset from the device manager through google. Since then, the phone has been found. In the off chance that the factory reset did not go through, as the phone was offline or dead,is there any way I can undo this? Also, how annoying or difficult is it to re upload apps, music, etc after the factory reset?
Yes. You can do it easily.
First Make sure you didn't have any Sim Card inserted in your phone and go away from any possible wifi area (incase if you did turned on Wifi or Mobile Data).
Then simply remove your Google account through Android Settings and try to use another Google account. (this works for all case)
This can help you to get your phone being formatted.