"Why did he opt out of his contract?"

As I understand it, he did this based on the knowledge that SF wasn't going to play him, and so he wanted to get on the market earlier as a free agent.  So, no, he would not still be playing.

...You can debate the merits / wisdom of this decision, but I would assume he thought that, as an NFC-winning and NFC-runner up QB, he'd have at least _some_ value on the market as a free agent....