Of course you did the right thing, unfortunately now you have to deal with the fallout from idiots who don't think about the possible consequences of stupid actions.
Personal experience:
DMs husband (so my FIL) many years ago he was hit by a drunk driver, thrown nearly 100m along the road, died twice, has brain damage, major back damage, other bone problems etc. etc. etc. (The driver was back from the armed forces on leave and was speeding home to see his family, which he missed greatly. Fine, but he'd spent hours in the pub drinking before driving home drunk to go and see them, if he was that desperate to see his children he wouldn't have gone to the pub - that is a whole other thread!)
A friend (from school) who made our wedding cake. In her early 20s was on the back of her boyfriends motorbike and a drunk driver smashed into them, injuring him, killing her. A life changed and a talented life wasted.
If someone had reported these drunk drivers and the police had stopped them from driving, many lives would be different now. Not just the fact that someone wouldn't have died and others wouldn't have been injured, but many relatives and friends wouldn't have been affected by these accidents. If I knew someone was driving drunk I would not hesitate to report them.
You did the right thing, just remember it is not your fault he is being prosecuted, it is his, and only his, no matter what anyone else says. From someone who has been affected by drunk drivers , thank you for reporting him.