As has been mentioned, until he actually got on the seat (and in a split second started the bike and ran) they wouldn't have been able to charge him with much that would have acted as a deterrent, or better yet, got him off the roads.
The resulting situation was basically a result of a legal requirement that allowed him to get to the point he did. Had the cop prevented the whole situation before he even got on the bike he couldn't have been charged with DUI. He'd still have his bike, he'd still have his license, and he'd still have an unblemished driving/insurance record, so in the end he'd probably just continue doing his drunk riding routine until something did happen.
Its a damned if you do damned if you don't situation. I'd side with the police on this one.
They had reasonable-cause and resources to search for and find the bike and they already waited for him so we're talking about a change of tactic.
Instead of waiting in the shadows and lighting them up when he exits the bar (or worse, when he swings a leg over the bike) they position a cruiser to block the bike in and wait on him. Maybe they send a couple of cops into the establishment to locate him and ask him to step outside for a chat.
At worst they miss the impaired riding/driving charge. Or perhaps they use that reasonable-cause and witness accounts from the previous bar to issue a breathalyzer at that point. If he fails, they take his license and impound the bike there and then. Maybe the charge sticks, maybe it doesn't. Regardless, the guy would have been kept off the road that night, the public would have been safer and he may still be alive now.
I don't feel like the public safety was served by the tactics they (apparently) used. Again, not trying to defend drunk driving or question the legality of the police actions, just suggesting that different tactics may have resulted in a better outcome overall.