The USA does have all of the technical data packages so in theory we could probably get domestic suppliers to make the components we currently get from the UK but it would take several years. The reverse isn't true, though. The UK simply no longer has the capacity to support such a complex program on their own. They sacrificed their defense industry years ago and accepted dependence on the USA so that they could fund social programs.
[1] https://en.m.wikipedia.org/wiki/Global_Combat_Air_Programme
They are starting to /design/ it now. Tempest is supposed to enter service in 10 years' time, which I will believe when I see it.
If that's the case they maybe they would be able to help the other partner countries develop the parts that they would otherwise require America to make.
As the UK is also a Level 1 partner if they were so inclined they could provide the resources necessary to allow lower level partners to operate and maintain their F-35s?