It's orbiting at the Earth-Sun L2 Lagrange point, with a perigee of 374,000 km
While we can put astronauts in space, we don't currently have any orbital vehicles with on-orbit satellite maintenance capabilities, since none of them have airlocks
The latter could very well change over the next few decades though, and the former may become economical, so I guess it can't be entirely ruled out.
But the landscape of the space industry is changing very rapidly. With a fleet of hundreds of reusable rockets floating around, the accessibility of the Hubble may change.
Of course, at that point it might be better to just send up a bigger instrument.
There's no mention of lifetime for the cryocooler @ [1], but if that thing becomes ineffective for whatever reason (helium refrigerant leak?), I think the telescope becomes somewhat useless.
[0] https://en.wikipedia.org/wiki/James_Webb_Space_Telescope#Lau...
[1] https://en.wikipedia.org/wiki/MIRI_(Mid-Infrared_Instrument)...