For future generations of missiles, recent events might encourage the UK to make buy/build decisions in line with those made by France, and I would personally be very pleased if we did. It's not at all good for us to rely on the US to make things that we could build ourselves, if we actually tried.
But: there's no real possibility of the transatlantic defence alliance suddenly completely failing, and we shouldn't allow the mercurial temperament of the current president to make us think that there is.