Can't remember any "hard facts" of the top of my head, but a quick look on Google yields a couple of links that relate to the upgrade the Sea Harrier was meant to get - JTIDS et al:
This one about ERA and
this one from Ultra. I also remember that Aerosystems International were also due to be involved, and were recruiting for people to work on the upgrade.
The fact that it was intended to upgrade the FA2 suggests that it was both intended to stay in service for quite a while, and that the Command considered it to be important for the RN to have the best possible air defence. If it wasn't important, why plan to spend lots of cash on it?
Look at the date on the first link. On that day, could you have predicted what would happen the next day? The world can change a lot in a very short space of time. If history teaches us anything, it is that we cannot predict the future with any accuracy.