You keep labouring under the presumption that him returning a positive drug test relates to the accident. I don't know any more about this case than you do, but I'd be surprised if it does. He wasn't reported to be drinking. That's far worse than any drug I know of. Even LSD.
You're more likely to veer across the road because you're not paying attention. More likely he was tired or looking at his phone. Or playing with the radio. Or whatever. Not paying attention. We don't know.
You don't get charged for any of those. Well, only if the cops catch you looking at your phone. Which they didn't.
So in reality there are 3 aspects to this case:
1. Driving without a licence
2. Returning a positive test for an undisclosed drug.
3. Having a prang.
4. Was he driving recklessly?
The courts are chocked with 1 & 2 every day. It's not newsworthy unless the perp is famous.
The prang is an accident. He'll get sued for damages. And because of 1 & 2, he'll probably have to foot the bill himself. Unless
@Nashy is right and the car is covered, not the driver. I'm not sure I'm convinced about that one.
We have yet to hear why he veered across the road, but no doubt his lawyers will be trying to take 4 off the table.