Typically when something is "deleted" it's actually earmarked to be over-written and its visibility removed, but remains present until enough additional data is added to the memory to require the space occupied by the deleted file, at which point the file is over-written.
So, if you've not recorded any more since the deletion you may be able to recover the file using 3rd-party recovery software (there's probably free stuff available online). I've done this with camera images before using the recovery software supplied with the (Sandisk) CF cards used by the camera.
How likely you'll be able to do this depends on how accessible the memory is - is it built into the camera or stored on a removable, standardised memory card? If the latter you may have more luck plugging the card directly into a card reader while attempting to recovery.