Yes, you should definitely have branch protection turned on on main, I kind of assumed that went without saying. But to actually lose your entire git history would require both having no branch protection and having every single developer on your staff be in the regular habit of force rebasing their own branches on main. If a single developer does a double take when they're told that their branch has a different history than origin/main, then you probably didn't lose more than a week of work.

Also, it's worth noting that this dead code will almost certainly not get reused wherever you decide to store it, so it's best to keep it as far away from zombification as possible, even if it's not the safest place.