If he isn't hurting your cap and isn't usingup a roster spot then keep him around. He is cheap and good. If when he can come back you are in good shape then cut him.
They can negotiate a deal anytime they like I think. The thing is in most cases you want to hold them in the low RFA levels. But if you sign them longterm before they make themselves into stars they can save a great deal of money.
No matter what Pitta has lost a ton of cash. His market value is way down until he can prove he is back. I wonder if he would be willing to sign a 1 yr deal to show he still has it.