Hi and welcome!
I've never had experience with eye surgery involving sequestrums, but I do have a cat, Miss Maggie Moo, who had two grafts on her one eye. (She only has one eye -- the other was removed.) Small sequestrums do fall off, but the larger ones often need surgery since if they fall off the eye may rupture, which, believe, is not something you want to experience. If the sequestrum is deep, they probably will graft the area to strengthen the cornea and prevent rupture. There is a 90% success rate for grafts (Maggie was in the 10% the first time

). The success rate depends a lot on the quality of the surgeon doing the operation. Make sure the vet is a Diplomate of the American College of Veterinary Ophthalmologists.
Assuming they have to do a graft, the aftercare with a graft is tedious but effective. You will be giving eye drops 4-8 times a day, 2-3 kinds, for several weeks as the graft grows in place. Then the drops are slowly phased out and after about 2 months, you are down to 1 drop a day. You and Oscar will get used to the eye drops in a few days -- he will hate them, but a treat afterwards will help him not hate them so much.
Now, with Maggie's graft, the tissue came from her eyelid, so it never will be clear. Presumeably if Oscar needs a graft, it will come from the eyeball itself and once healed, it will be clear and totally functional. Even with a cloudy graft in the middle of her only eye and scar tissue from previous infections, Maggie can motor around with no problems.
I wish you and Oscar the best in all this.