It should just re-deposit like any other award that doesn't clear. Miles + money should go back within a few days.

Website says within 7 days - my wife and I failed to clear on an upgrade Award domestically and miles were back within 3 days - but that's he soonest I checked so might have been faster. No $ involved, though I suspect they are processed at the same time and because the banks take a couple of days to process he refund, that takes a bit longer.

If you do so take a buy-up, I'd keep the receipt just in case, and if the miles don't go back withtin the stated 7 days, call. You always have the receipt to backup that the award didn't clear. And should be no redepoost fee - when an award doesn't clear, it doesn't clear - whether you bought up another way or we're still on the list with a full cabin shouldn't make a difference. The only time a redeposit fee should be charged is if you call in to cancel the award.