Would it be okay for my dad to have another pvr eye surgery after vitrectomy?

It's ok: If he needs it. Pvr (proliferative vitreoretinopathy or scar tissue) can grow back after vitrectomy surgery, requiring yet another vitrectomy. Ask you retina specialist. You could always get a second opinion.

Common for PVR: Pvr is the most common cause of failure for retinal detachment surgery. Some patients have a very active healing response which creates scar tissue that pulls the retina back off. Once pvr occurs, it needs to be treated with vitrectomy and possibly a buckle and silicone oil. It is possible that multiple surgeries will be needed to stabilize the retina.