prob not, but i would actually like that. i think igor rocks and wish we knew what happened to him. if the rumors are true about a TF prison in TLK, i want to see him in there to.
Although I believe it's highly unlikely he's one of the new decepticons we've seen I would love to see him return. Megatrons entire camp from DOTM is something I'd like to see play a role in megatrons return. We know he was raising hatchlings there which was a nice continuation from the hatchlings from ROTF and it would be cool (but most likely won't happen) if Igor managed to raise a few of them in megatrons absence.
While he didn't die at the end of DOTM, I'm highly doubting he becomes Onslaught by the events of TLK. He's either already been hunted down and killed by Cemetery Wind sometime after the Battle of Chicago, or he's just off doing his own thing. Plus, I don't think the writers would come up with such an idea.
If the new movie aims to connect any missing loop holes, some closure to that silly head idea from TF3 would be good. Then again I can also see why it would be ignored either way.