Most secure way of sending bitcoins from bitcoin-qt offline wallet
I don't think that is really a problem, but first of all why do you want to use a Linux Live boot? Is that to disable possibly installed malware? When you send your transaction make sure that you install your temporary bitcoin client on a persistent drive, e.g. not on the computers RAM (this will take a lot of time, so better clear out your computer instead of this approach). Your private key will be generated before you send your transaction, so you can't lose it when power shuts of.

This won't save you of course when power shuts down and your hard-drive crashes at the same moment, but when you are dealing with large amounts of bitcoins you could probably use some RAID configuration (e.g. RAID-1) for your hard-drives and still be fine. Or you could buy an external power source as backup.