I am relatively new to RoR. However, I'm a bit concerned that losing this file will present some problems if you aspire to host your app on a server other than the one it is currently hosted on. For example, if you had a mind to host the app in Heroku, you would need to run your migrations in that environment.
If you are not terribly far along with your application, it would be best to start over, take care not to delete your migrations, and put your app under version control so that you will have a fallback should you run into this problem in the future.