Will my pokemon ever come back?

Eventually, someone will find the gym and take him down, and it will be easy because his motivation will be nearly nil.

If that doesn't happen in a few weeks, start asking friends who play if they could take it down for you.

I had a Nidoqueen stuck in a gym for 109 days. Not really a problem, that, but that gym is still my highest on points, despite no victories, no berries, and never going back there. I reserve Snorlax, Blissey and Chancey for the busy gyms, ones I know I might not hold for an hour.

With the current GYM Style...
I never put a Best Defender Pokes in GYM because it is useless when the CP are decayed... Even a low level trainer can destroy a L40 Blissey when it is low motivated...
So I just put a something Rarer pokes or Shiny as Gym Presentation.

@Topic : He will never comeback unless somebody KO him/her...

You can just make a second account, go back there and kill it or ask a spoofer do to it.

Eventually you will get it. I had one in a rural small town that was away for 48 days before someone finally knocked it back out.

It won't come back if no one fights it.

Hopefully you know a friend who lives nearby or is willing to make the trip?

After your badge hits gold, post the GPS coordinates of the gym online and you will probably have it back within a day.

Spoofers will take it down eventually. I base this on my own story. I'm pretty sure I've been the only legitimate player ever to put a Pokemon in this gym on the middle of the Neil (Egypt).

I had to specifically ask the boat driver to make a stop at this point for me to be able to put a Pokemon in. To my surprise the gym was full of other Pokemon within 24 hours. Within 48 hours the gyms was knocked, right...

If you are really concerned and want it back, then go to R/POKEMONGOSPOOFING and ask a kind spoofer to return it for you. People do this all the time.

You will need to get the coordinates for them.