Can't believe someone hasn't posted this yet, but in today's presser, when asked about Mone returning to play some time this season, Harbaugh didn't shoot it down and said "it's possible". I don't know exactly how the question was framed as I ran across this on the Twitter, so context may be missing. But, commence speculation! And commence putting a Dumb and Dumber captioned picture in this thread.
Personally, I think his return, even if physically able, probably would depend on how long the season runs, and what the stakes UM is playing for at that time.
Here's a link about it on 247: