Lots of regional guys get picked up by ANG units, so it isn't that unusual to do what you’re contemplating. I'm in the process of doing the same thing, but my situation is a little different than yours. And it isn't really a significant pay cut for you by my math. Regional FOs make $40k-$70k. Most regional CAs make $50k-$120k. 2-5 year (your demographic while you'd be on mil leave) regional CAs make $50-$90k, all of which is taxable, and your medical costs money as well. As an O-1 you'd make $3,108 base pay (taxable), then allowances that are all non-taxable: $260 in BAS, $1100 in BAH (Sheppard), and $125 flight pay. So you are only paying 12% tax on around $38k (~$30k after the deduction), but taking in around $18k tax free in allowances. So, first two years you'll take home around $50k, and probably $70k after you make O-2 with more than 2 years, and $90k as an O-3 over 4 years, again all with lower tax liability and medical costs than an airline job. After taxes/medical, your regional CA pay wouldn't be that much more. If the exact numbers are important to you, you can easily make a spreadsheet with the pay differences for each course of action to compare...most of those above figures are WAGs.

Where the real money difference comes is when you'd get picked up by a major in each scenario. You can make spreadsheets with various variables and make an educated guess as to how much each scenario will vary with lifetime earnings, retirement pay, medical, etc. But there are so many unpredictable variables, which make that a very difficult calculation. If you went into the military, you'll never know exactly when you'd get hired at a major as a straight civilian. Also, as an AF pilot, you will be significantly more marketable and a “top tier” candidate for DAL/AA/UAL/SWA/FDX/UPS. There are thousands of regional CAs out there…there are fewer mil pilots (and even fewer mil pilots with 121 experience). Maybe you’d fast track to a major from your regional, maybe not.

Do what you want to do…IMO the lifetime pay is a wash/impossible to determine a significant difference. There are benefits to being in the military that you can’t put a monetary value on (brotherhood/friendships, experiences/stories, pride, etc.). Sounds like you really want to do the ANG thing. How much would that suck to be one of the guys chatting to the former mil pilot guy you're flying with saying "yeah I wanted to be a military pilot, but didn't for X,Y,Z reasons” and at that point you’re too old and have to live with that regret. I've flown with a lot of guys who regret NOT doing the military flying thing, but I've never flown with anyone who regretted flying in the military. I know a guy who will be on 3rd year JetBlue pay going to UPT to fly fighters in the ANG. Sure it’s a pay cut, but where/when else do you get to fly fighters or do anything like it? Nothing you will ever do in life can compare to the experience/challenge/brotherhood of being a mil pilot…especially a fighter pilot.