Did he leave Shameless ?

Yes he left

He left due to prior commitments to Teenage Mutant Ninja Turtles 2. When the first TMNT happened, he was upset when he couldn't audition for it because he was tied up on Shameless (which was shooting at the time). But then the first movie fortunately got pushed back, giving him his shot at auditioning at a later date, which landed him the role.

Since TMNT ended up getting a sequel, and he was playing a prominent role in the movie, obviously he was already committed to it by default regardless of when it would start production. This was why he couldn't sign up for the 6th season of Shameless.

Time will tell whether or not his departure is "for good," because he can always come back to the show if his schedule allows (and if he's interested). Even John Wells, the creator of the show, said that he'd welcome him back if he wants to come back. So, really, it's up to him.

To be honest, though... I'm not a big fan of the current season's writing for ALL characters. If it continues in this direction (like Dexter's 6th, 7th, and 8th seasons), I don't think Noel Fisher should come back. They're just going to ruin his character like they did with the Gallaghers. If everything takes a turn for the best, I'd like to see him back for sure, as well as Shiela, Karen, and definitely Mandy!

Yes as you'll see on imbd he is listed from 2011 until 2016 no more mickey

Except that the new season starts the beginning of October so 2016 would be accurate. They wouldn't list 2017 until it's been renewed for next year. There are a whole lot of fans of Gallovich & as dysfunctional it was, it was the most stable & positive relationship on Shameless. Strangely, Gallovich is also a role model for young gay men as it shows loyalty & love can overcome what difficulties test the relationship.