JWST is a massive origami like Rube Goldberg machine. I hope they get it working properly and that it doesn't fail. Because unlike Hubble, no one is going to make a trip to repair it this time. It will be just too far away.
No one can. The Shuttle was the only craft that could fix and launch the Hubble. The Web will be parked well beyond the range of any current manned craft. Sadly though it will bring unique capabilities it’s not a replacement for the Hubble which is in a death spiral right now.
I have seen proposals - not just the stuff of power point rangers, but real work analysis and budgeting done - to have Orion service the Web. I don't believe the plans will work: not because of the technical side, but the cost. The SLS is mildly nuts for price and Orion will only be using that launcher currently.
The next really big American optical telescope will be the Roman Space Telescope in 2027. This one has a bit less risk as the mirrors and bus are already built. It's more about getting the instruments done. Seems its IR also though. It/She will orbit at the earth-sun L2 point.