Just got the FLR (M) extension so we were looking at my wife completing this sooner rather than waiting until just before ILR. As we've got 2.5 years, will see if there are any changes afoot in the next 6 months or so.
The Life in trhe UK test was brought in by the new Labour government and I can't see this ending as the UK's other main political parties support this too.
Questions get changed on the test. e.g. when Labour brought this Life in the UK test in, they put questions on how to claim benefits from the UK and it stated something like, that Tony Blair (the then Labour leader) was benevolent. With Labour voted out of government and the two political parties, the SDP-Liberal Alliance and the Conservatives, now in government, the benefit questions got replaced by history questions.
The Life in the UK test doesn't have a time limit. The changes in the questions last time, didn't invalidate the pass.