There actually is one in the plugins directory, disabled by default.
You can enable it with:
sudo chmod +x OSPi/plugins/system_update.py
But it only does a git pull and will not handle this situation. It will be easy to fix.
I am currently working on a new plugin management system that will make things a lot easier. I will include an updated rev of the system updater when that is released. Hopefully within the next couple of weeks.
Dan