Had vitrectomy and scleral buckle for detach retina gas bubble at 40%. but i see grey patch in central vision and it moves with eye movement. will it go way in time?

See your doctor who did the procedure. He could give you the best answer. Good Luck

There is always some permanent damage following a retinal detachment. With a 40% gas bubble remaining in the eye, it is not possible to determine from your description whether you're healing adequately or whether there's a problem (subretinal fluid under the macula). If you have concerns you should have your surgeon evaluate you.