Even longer for it to actually power up and start "working." Really excited for it, but feel like something akin to this hubble issue happening with the JW would be disastrous.
And not just disastrous for James Webb, disastrous for the possibility of future funding of space missions in the near future. Congress would be much more hesitant to fund anything as large as the James Webb in the future if it failed.
Not if China starts funding such things as many in the US Congress would not want China to have more advanced assets in orbit and would authorize funding to make it work.
It's hard to say, but for the JWST the design and R&D seems to have been the easier part [1].
In general it's uncommon to build a replacement satellite after an issue. Either you make a backup from the start, or you start over after failure. Making a one-off component often isn't all that much simpler just because you've already done it once a decade ago (and some parts of the JWST should be about a decade old by now). And if you commit to doing that all over again, might as well update the entire design to new capabilities and requirements.
Unfortunately, even if we do develop the capability to get astronauts out there, the Webb is constructed with a lot of adhesive and layered components and is basically impossible to service in space.
I think the best we could hope for is maybe being able to drill into the liquid helium tank and refill it - which is the ultimate determinate of its useful lifetime (that and propellant, but I'm led to believe the liquid helium will run out first).
Probably a moot point though: by the time we can get people out to do such an operation, I suspect a reduction in launch costs might lead to a much cheaper space telescope you could just drop off instead.
There is no consumable liquid helium. Past space telescopes have used consumable coolant, but JWST has a closed refrigeration system to cool the one instrument that requires active cooling.
If all goes as planned, the limiting factor is propellant. And the propellant tanks have the ports for on-orbit refueling, in case there is ever a desire to develop a robotic servicing mission for the task.
If the R&D is done anyway, why not just wait and build a second telescope if the first one fails? I don't see why that would be any more expensive than building a backup ahead of time, and it means if the first one fails due to an undetected design flaw, they have a chance to correct it.
It’s cheaper to build two at the same time than shutting down production for years and trying to build another one. Tooling doesn’t last forever, and the process and skills required to build one can help you build the second one cheaper. But if you wait, that knowledge is often lost. For example, we have no way to build a Saturn V rocket today even having spent R&D and NRE decades ago.
Same reason NASA built the Space Shuttle Endeavour with spare parts left over from the others, instead of building it from scratch. People move on with their lives, and the facilities that manufacture these things do too. Assuming everything was well documented it should be possible to recreate the tooling and train new people, but that's much more expensive than building two in the first place.
