Pretty small surface area to fix to, I think I would flatten out the broken off tab with pliers or a vice, then reattach with JB weld or similar like mentioned above. It will then sit higher than the other side but that shouldn’t be a problem.
Flattening it out and attaching to the bottom of the baseplate will increase the area you have to worth with.
Other alternative is a new larger piece of metal attached to the bottom of the baseplate but then you also have to drill and tap it.