If the ticket is not flexible, you can't cancel & refund it.

Seriously, I think you're worrying a lot over nothing. Not once in nearly 6 years of pretty regular WT+ travel have I ended up in a middle seat (and that applies equally as Blue, Silver or Gold!).

It seems to me to be familes/OpUps/people who aren't clued up (and armed with the advice above on Manage My Booking and OLCI, you now are ) who get stuck there. I've always had an aisle (except when I've specifically chosen a window myself). Really, don't worry. If you're still paranoid, then Dave Noble's suggestion is the best one - do it over the phone with a real live agent and get them to look at the seats first before you book/pay. But as I said, this will cost you ($15, maybe more, not sure) extra.

Phil