Refusal to take a test is, in most jurisdictions, equivalent to conviction. How much he drank would depend on his metabolism – and it would have no bearing. If he drank a quart, but had a .07 BAC at the time of the accident, he wasn’t DWI. If he drank half a shot, but had a .09 BAC 3 hours later, he was driving illegally. Push on the refusal – that should be grounds (along with a .07 90 minutes later) for conviction and, coupled with an injury, at least a long suspension of license, if not revocation. (See if you can get to speak to the DA or ADA handling the case.)