Hit another car but they drove off, unsure if collision will cover damages

This is in Illinois, been driving for about a decade and never had an accident. I rear ended someone about a month ago, and they drove off without wanting to file a police report or get insurance involved because:

a. the only visible damage was to my car b. I'm pretty confident they were drunk and did not want to risk cops showing up and risking a DUI

I didn't get insurance involved at the time because when I asked a couple friends they figured it would be best to not file any report since there was no other proof of the car being involved. Essentially that it would look like I'd hit and run someone.

I also thought that the repairs would only be maybe 1000-1500 at the most and I could eat that and not risk my insurance premiums going up. It turns out after having my car in the shop for a month there was a lot of internal damage and the cost was a little over 6000. My collision policy is 1000 deductible so theoretically I could send them the bill and get back about 5000, which would be pretty huge for me.

But since I didn't file a police report at the time or report it to them I 'm thinking maybe I should just do nothing. 5000 would be great but they could easily just say you didn't report it to us, you get nothing, and your rates go up now. Does anyone have any advice on whether it's worth trying to use my collision policy here or just move on?