You can pick up a full set of replacement parts for $12 + shipping from BOA if you want extras to have on hand. If your BOA system actually breaks they will sent you replacements for free. There was someone on the mountain who would have been able to fix the boot for us if we'd had the parts, but the store there did not carry replacement BOA parts. He did mention that if it had been a cable that broke he would probably have been able to tie it back together as a short term solution to keep the boots running until we could get a new cable.
btw. he would not have been able to tie the cable together.
If you are the smart, plan-ahead type, you can just email BOA now, before your shit breaks, and carry it around in your gear. Even tell them your ratchet spool jammed/exploded so they send everything (if not specific, they will only send a cable). Don't pay for shit.
That's what I'd do if I ever have another pair of BOA's, which I won't, because I'm still confused about besides the addition of technology, r&d, material, and money, I don't understand what improvement they provide over laces. And don't say they are faster, because while they may be slightly quicker in the morning, you will see many people (myself included) who will fuck with them all day long just because they can. I don't even untie at lunch in the lodge because my boots are comfy and may as well been laced by magic lacing gremlins for all my feet know.
Tying traditional laces seems really easy to me, but maybe i'm like the fucking Michael Jordan of lace tying.