They can, depending on the settings you use. You and person A used to be friends. You failed to say hi one day and A got mad and deleted you and blocked you. You and A can't see or talk to each other anymore. You and B are still friends, though A's friend C and you never were. If you post something public then B and C can see it. But if you post something to friends only, then B can see it, A and C can't.
Deleted messages? You didn't say that in your OP. Are they really deleted? Just because you unfriend someone/block them doesn't delete your posts. There is a "game" that I know some people play where they look at their older history posts. You can look at the people who liked something or commented, and then see if you are still friends or not. I know for a fact that some people have blocked me but still have posts on my wall. Just because you are blocked doesn't mean your comments are deleted.
If however you legit deleted them, then no one can see them. Even you.
Then aren't we back to my original post? If the posts are public and they aren't blocked then they can see it. If it's friends only then they can't. Unless they are a friend. I'm really not sure why this is an issue.