That occurred to me too. Something in the nature of a "functional alcoholic." However, that is belied by his history at UW and USC of uncontrolled public drinking.
The very nature of alcoholism is that it doesn't get "better," or "more controlled." It inevitably gets worse.
Sure, a guy that makes a public fool of himself, as did Sark, could withdraw into the bottle and avoid such public displays in the future. But that requires actually withdrawing from society, which Sark has not done.
But Sark has shown a past tendency to drink at the worst possible times and once that "tendency" is exposed, if the drinking continues, the public displays will, also.
So, it seems to me unlikely that Sark is going "AWOL" to drink. It would inevitably evidence itself in other ways. What's more likely is that he has to take some time off to handle shit with Loreal, or whatever, and to avoid drinking in the first place.
Given his history, I would be surprised if CDC would tolerate really completely AWOL, that is unexplained and unexcused absence. That's also contrary to the recovery mindset of honesty and admission that trust has been betrayed.
I would believe, however, that his absences were explained to a select few who kept a pretty tight lid on it in the belief that offering explanations violates his privacy and invites more controversy.