You might not be able to do much with it on the phone. You could try transferring it to your PC, and see if it will play with something like VideoLan. That's rather good at dealing with broken and incomplete video files. VideoLAN - VLC: Official site - Free multimedia solutions for all OS!
That's if anything got stored before the phone lost power, and it's not just a directory entry.
You can also check that it's not showing as zero bytes, if it is I don't think you'll get anything back.