Update!
Short version: Miles (supposed to be) reinstated within 24 hours!
Long version: Called Frontier and I was told the exact same thing as last time (his miles expired b/c 6 months of no activity, we could fly within 2 months to get them back). I threatened BBB complaint, the lady passed me on to her manager. Manager said exact same story as the first lady, I threatened BBB complaint, she talked w/ her manager, and now they're promising miles will be reinstated within 24 hours. She said I'll have two months to use them (which amazingly is the EXACT same date that the stupid website told me for months on end was the date the miles would expire...March 18, 2016!!!). So I asked if his account online would say that date as the expiration date, and she said 'no, it'll say six months from last activity'. Ohhhh their website is so functional and helpful! Ha! Then she said 'so that will be sometime in April'. What in the heck is she talking about?!?! How is two months from now April? I don't know, but I'm booking travel tomorrow and closing this account. Thanks for the help.