How would they go about bringing the telescope back to Earth? Does the maintenance of satellites occur on Earth often?

I believe that's only been done once during the Shuttle flight STS-51-A, but wasn't a telescope. The problem is the only vehicle that has ever been capable of doing that was the Space Shuttle and the operation was very dangerous + expensive.

The only case of repairing a satellite ever done by Humanity was Hubble's repair. That mission was so risky, there was a second Space Shuttle standing by on another launch pad totally fueled and crewed so they could rescue the crew of STS-125 if something went wrong.

SpaceX believes they could eventually perform operations like that with Starship once it's developed, but who knows if that will ever end up happening.