Unfortunately your tech is right. You just cannot diagnose something when it isn't broken. Intermittent problems are the worst things to deal with. They always have a habit of behaving themselves when under scrutiny.

If you are not willing to wait until it fails, you will end up spending lots of money and replacing lots of parts that don't need replacing.

It sounds like maybe you had another post somewhere that explained more about what happened to the car. If that's not the case, there's not much information in your post to go on. Since there was a wire severed, can you find any other loose connectors or other problems in that area. You don't say how it was severed so there's just not alot to go on here.

Sorry to be the bearer of bad news.

Good luck,