It's a real pain when this happens but as mentioned above, Vegas should prompt you about recovering the file when you next open the program. There is a basic 'autosave' option on Vegas (every 5mins I think), but it's really best to get into the habit of manually saving (ctrl+s) every few mins, and possibly incrementally saving at longer intervals eg. filename001, filename002, that way you can always go back to a previous file if something gets screwed big time.