As a non-elite your access to saver awards would likely have been limited anyway. You're probably thinking of these 100k miles in the context of a different era. Likely the most you would've gotten would have been two standard domestic economy seats and a small handful of miles left over. In the grand scheme of things, you really haven't lost all that much. Certainly not what you're wanting to hear right now but that's probably as close to a bright side as you're going to get at this point. I'd be fairly surprised if you made any real headway; UA just recorded a huge bump in revenue from expired miles and so that's factored into their stock price at this point. To go around giving back expired miles they'd have to take a charge down the line. Not likely!
(For the record, I think an 18-month expiration schedule is overly aggressive but, as has been pointed out to me in a different thread, it's pretty much industry standard practice at this point).