There is a little bit more of decision to be made than just "he sucks/he's hurt a lot, don't pick up the option". From what I understand if we pick up his 5th year option it's a little over 9M, but if he does indeed have a stellar year, then the cost to franchise tag him would be a little over 15M. So if they believe in him, then save the 6M and pick up the 5th year. Like Stephen said, the wise move is to see what happens in the draft obviously. I agree with a previous poster that said they likely already have a good idea of what they'll do in each scenario, whether they get a LB early or not. I think it's a pretty tough call, since he's shown the ability to worth 9M+ but also possibly not being worth a contract at all.
I'm no cap guru, so those salaries are based off some quick googling.