Actually the final walk through in most areas of the country are NOT a condition of the sale.
You might want to review your contract with a real estate attorney and ask the question. In my opinion, and I can not say for sure, I do not believe this is the case.
I can see arguments going both ways, however It is my opinion that it is an informal check up on the house.
Seller is to allow access. The seller did not make it snow. Just the same if the streets were flooded, I don't believe the seller has to clear the streets. Have to make access or allow access may be the key words to recognize here.
Just one opinion I am sure there will be more.
So Cal Homes Realty