Old free transfer players are always a risk to sign. If a player sells a player in the age of 31-33, you know he won't retire this season, but if it's a free agent, there is no such guarantee at all.
Whether you sack him or keep him, it doesn't matter, you'll have to pay the same salary regardless. You may as well keep him around till he takes up a spot that you need for another player in your reserves.