I've seen Harrier II+ in build, and reckon even with acoustic vibration they have a long life !
Quite a lot beefier than GR9 etc.
There are also monitoring systens such as EUMS, and I'm quite sure RR would provide support with zero-lifed engines.
The Harriers are all tired aircraft now sadly, and are quite a way down the path of fatigue enhancing structural upgrade. Having worked with both types and had full access to the build drawings for both, I can assure you that the HarrierII+ does not have a 'quite a lot beefier' airframe and with the Frame 29 and 19 structural enhancement mods carried out, the GR9 is arguably stronger in many ways. The GR9 and T12 fleet are also now modified so that the majority of airframes now have the FMCS (Fatigue Monitoring and Computing System) monitoring systems fitted to the aircraft.
As anyone who will have seen full power ground runs of a Harrier on Tie-Down, they shake and rattle theirselves to pieces, and this manifests itself with structural issues in the aft end and tail areas, and there is only so long you can realistically and cost effectively keep 'patching this up' Unfortunately, the II+ suffers from the exact same problems as any other Harrier in this and other regards and is itself now a tired fleet.
My own opinion of course, but should we find ourselves in the market for an F35 alternative, I personally cannot see the logic or argument for purchasing a fleet of tired aircraft which are frankly ill suited to the task, versus a fully fledged, and comparatively modern genuine multi-role aircraft, such as the F/A-18?
Flipflopman