Following commits is probably good enough, but perhaps we could have a changelog file where we specify what we changed. doesnt mean the exact details as to the texts etc but more of a overview of changes so that people can easily see. Very much like the changelog of software where you have highlights of changes rather then the entire commit tree to go through.
I think it's absolutely necessary. And as Muppeth say, it doesn't need to be super detailed, but just a date and maybe a good brief and descriptive couple of words as title.
Deleting a branch is permanent. It CANNOT be undone. Continue?