Get your ATPL!! It at least gives you options. I assume you are leaving at your AFPS15 exit point of 40 years; if not, and you are taking an option, you can give two years notice (with the ability to, usually, easily recind), giving you access to resettlement. You'll need to do your 14 exams, with Bristol Groundschool crammers being the answer, but with a combination of one ELC plus your Resettlement money (it's around £500 without as many restrictions as an ELC) the course should only cost a few hundred bucks. Also, by doing the crammer and exams whilst on GRT this entitles you to accommodation, transport and subsistence; check the night subsistence rate with your friendliest adminner and book the best hotel you can. You also need a class 1 medical.
You should be able to open your licence in the sim if the E3 is recognised by EASA, although not sure what level of sim the E3D has. If not, on the aircraft; you just have to pay for the examiner. Even if you have to do it outside of work, it's not prohibitively expensive, these guys should be able to assist and provide further info:
https://www.ukflying.com/
Leaving in the last few years has improved my lifestyle (and wallet) immeasurably, but you do, of course, miss the camaraderie of Sqn life. You don't miss the desert! There are outfits out there in the airline and corporate world who will value your experience; you don't have to become a two stripe seniority nigel, although that lifestyle may work for you. As mentioned above, Jet2 is very mil friendly.