Axeman, you sound like you run your company like I run mine. Although I do have a job description (do everything and then do what I tell you to do ) written out. It was required by my workers comp and liability insurance carrier.
The wrongful termination greatly varies by state. Alabama (my state) is considered an "At Will" state. which means as an employer I can hire and fire at will with no reason. I can fire for hair color or the color of your eyes. Sure, I can be sued by an ambulance chaser lawyer, It will cost me time and money to defend the suit, but in the end I will countersue for damages because the written law backs me up in this case.
Should you decide to terminate, list NO reason, or an easy out would be failure to show for work or performance of duties (get on that job description list asap). Find out what kind of state you live in for the employment law.
I had a similar situation two years ago. I hired an aquantance I had known for years who after 10 years with his Company was the discoverer of the "at will" State in which we live.
Long story short- he had and on the job injury (shot himself with a nailgun in the foot) Per my insurance regs, I had a drug test run, and It came back positive for MJ. He said he smoked one joint the day before (his off day) and it was the first time he had smoke a joint is years (another aquantance of his gave it to him). It ruined our friendship, He could not understand why I fired him, all he could see was no income and looking for a job.
From my situation here is what I looked at to make my decision. He is now a KNOWN quantity. had he never been hurt and the job was completed, I would be none the wiser for is off the clock action. But now, he is a liability. Sure, " I only did it once, on my off day and will never do it again" and here is a BIG BUT, If he did and hurt one of my other employees, I am Vastly liable for his action because I now knew he did pot and came to work from his past actions. A lawyer would have a hayday and bury me and my family. All because I tried to give a second chance to someone. And a big increase in rates if I retained him. (the removal of the nail alone was over $26,000)
I am not saying you should fire your man for an off the clock DWI. I am saying you have to evaluate,have you ever suspected him of being drunk on the job, hungover from the night before. If you feel this was a one time event of a special celebration that he exercised poor judgement and choose to drive, maybe give him a second chance IF he is a really GOOD employee. If you have any doubt, cut him loose, as his actions will affect not only him and whoever he directly DWI's again, it will also affect your company, all the other employees (if you have to pay for a lawsuit)and YOUR FAMILY if you are sued because of his actions.
If he gets a lawyer and finds a plee deal to keep the DWI off his record. You can keep him as it should remove the liability of his future actions from you. That (I am sure) would take longer than the 6 month suspension. The termination is easy you as an employer can always "make" that happen for many reasons.