Welcome to the forum. I am so sorry to hear about your Marcus.
A friend of mine has a sheltie that has gone blind. Sadie gets around very well still.
Mary (my friend) says she does not plan on ever moving around any of the furniture.
Basically, Sadie has remembered where everything is. She can go down one step out of the side of the house to the backyard on her own. Mary does follow her out into the yard and stays there with her till Sadie does her business, then they both come in. I have seen Sadie do this. She is an amazing sheltie. To watch her navigate around you would never know she was blind.
Sadie does have her full hearing, though.
There are some members here on the forum that have blind and or deaf shelties.
Maybe they can give you some insight.