So if a community is type 3 (only members can post or comment), and a member that had posts and comments in the communities loses his membership his future posts/comments will be muted but his previous posts/comments will remain visible.

In this case, what happens if someone has already been currently muted in a community and therefore all their old and previous content has been greyed out affecting their visibility under the current rules?

With all these new changes in community Types that you are specifying, will they regain their visibility or will they continue to remain hidden?