The power was dropped during recording - resulting file wont play in camera or open in Vegas - Is there any software to repair or transcode ?

Have you tried to place it in the 'trimmer' in Vegas Pro rather than in the timeline?
I haven't had any corrupt XAVC files, but a couple of times I was given bad files in other codecs which I was able to place in the Vegas trimmer - and then select and drag non-corrupt parts of the file down to the timeline, eventually being able to reconstitute everything but the corrupt section.
Just something to try...

Thanks for the suggestion Dave but no luck with dropping it in the trimmer.