Generally, you'd need to replace the roofing above the sheets of plywood that are replaced. Make sure you have a good roofer who can properly 'blend' the new materials with the old. Basically, when you're doing the roof you start at the bottom so it's somewhat un-natural to remove this lower roofing without removing what's above it. Not that it can't be done. It's just not as easy as some other roof repairs.

IMO the risk you run cutting into the roof to replace the plywood isn't worth it to replace what's on that picture.