But I presume the telescope continues to be useful, if not necessary to the same degree. How is it likely to be used in future?
JWST can't see the same wavelengths of light. There's some overlap in near-infrared, but JWST doesn't see shorter wavelengths.
Lots of astrophysical processes will still be better explored with Hubble.
Even if JWST is just better all around for a whole class of observation, there are always more good proposals than available telescope time.
And there are always dynamic events to be observed, that nobody could predict.
The great thing about astronomy: for every fundamentally new discovery that requires a multi-billion-dollar spacecraft, there's another fundamental discovery waiting for a careful observer on the ground.
Hubble gave us some great views of a comet hitting Jupiter, but never would have been looking there if it wasn't for the dedicated search of ground-based comet hunters. Who needed thousands of observations, hundreds of hours, to see it coming.
https://en.m.wikipedia.org/wiki/Comet_Shoemaker–Levy_9
And it's not just the pros. Anyone has a chance to contribute significant new science. I know professional astronomers who got lucky one night, way back as undergraduates. Just happened to be there, and to know enough to notice something worth digging into.
Great question!