Ditto all the above but, there are so many variables with each horse that one has to evaluate everything everyone says, temper with a lot of common sense, then do something in the middle
I have one horse who foundered really bad in March, 2012. He never did go off grass but he does live in a grazing muzzle most of the year as I am in the Southeast U.S. where we don't see much winter.
Based on my own experience, which my vet was on board with, talk to your vet, put a muzzle on your horse until it's cold enough for him to see his breath, put a pair of trail boots with partial pads on him, and turn him out for 8 - 10 hours every day.
^^^^that is assuming you have ample acreage for him to forage across with his friends. My foundered horse has 21 acres of nothing but hills; he gets a lot more exercise, in an hour, than I could give him in a day.
I also have this horse on prescription herbs, which could be compared to the drug Thyro-L because his insulin is so difficult to control. The herbs are a crucial piece of this horse's formula for safe pasture grazing.
He eats tested grass hay and gets his vitamins/minerals from McCauley's M-10 Balancer which is oat/corn/soy-free.
Just one more piece of input to get your head in a tailspin. There is no black and white answer to your question; your horse's metabolism and how it reacts is the key. I have a second IR horse that has never worn a muzzle and never had a laminitic issue; he is controlled with nothing more than a strict diet. Go figure
Read and draw from how we all handle each of our foundered or laminitic horses, and find Plans "A", "B", & "C" from there.