True, you'll remain able to get the old version out of the repository, because it has all the past versions. If you intend never to change anything ever again, I guess that's enough.
Good luck with that.
It will be enough if they wish to have an unusable coin with confirmations being processed at a practically unusable speed for at least 2 weeks, and than slow as molasses for another 2 weeks. It may take many months with more miners dropping off with fear before they reach equilibrium due to the retarget limits set in the current source code.
This is why I was offering some friendly advice for them to get ready to create their own hard fork and migrate it to a new github so they have a chance of surviving during the brutal transition they will witness.
This isn't even going to address the possibility of an attack by existing miners either which brings up a whole other concern that they will need to consider.