You can do stuff like put the camera in a rad-shielded enclosure and use an imaging fibeoptic bundle to bring the light from the focal plane of the lens to the image sensor, but increasing its endurance will carry a massive weight penalty and a significant image quality penalty.
The other issue, as you have touched on, is what do you do with a heavily contaminated robot that needs sensors and control systems outside of it fully rad-hardened brainbox replaced? Its probably too hot for humans to work on, so unless its been designed for another robot to be able to swap pluggable modules, and has good enough onboard diagnostics to be able to identify what's failed, repair will be impossible. Writing it off, dumping it in a steel drum and pouring in concrete, and starting up a new factory fresh replacement is the sane thing to do.