Easy Street,
It may be in existence NOW, but how significant is the fact that in the SDSR document each and every ISTSR asset at Waddington has a specific extended OSD of either "2030/at least 2030/2035" except Sentinel which is "extended into the next decade?
That would mean it surviving until P-8 enters service, so maybe the second squadron? 5 Squadrons seniority would trump everybody else's.
Seniority only comes into play when a squadron number is resurrected, it has no input or affect on disbandment decisions.