Comparing a "standard" RAF transport Herc with the Hercs operated by the US Coast Guard is apples and cobblestones.
The USCG Hercs (and the Talon package, but with bad guys possibly involved) were designed and equipped for SAR /CSAR respectively and very little else.
So if its a "real" SAR Herc coming to find you, just wait an hour longer before you switch on SARAH or whatever you call it this week, PLB, ELB, annoying beepy thing on Guard?
And the Herc can carry and drop a lot more Lindholme gear than a Nimrod. Even chuck you a boat maybe.
Hmm, could we fit a bunch of side-firing artillery too? Not everyone needs hoying out of the Oggin.
Another route is keep the Nimrods.