I've gone through about 8 NHL teams so far and the only rostered player I can find that produced anywhere close to Borgen's level in the AHL is Scott Mayfield from the Islanders. He still outproduced Borgen though, but it's somewhat close. I have no idea about the guy though on whether he's any good..
That's a pretty good comparable, actually. Hjalmarsson is another guy who never really scored at any level but is an extremely valuable defenseman. He scored more than Borgen in the A, but not by much ( approximately 0.3 ppg vs. 0.19 ppg).
As you pointed out, these guys are extremely rare, and in general, such a pronounced lack of production is a red flag for any prospect. Having said that, I can buy an argument that his usage kept his numbers lower than these comparables, since Rochester was stacked with really good (in some cases, NHL-calibre) D.
At this point, in terms of his value as a prospect, the new GM does not have the luxury of trying to "figure out" if he can do it with another year in the AHL. He is just on the cusp of going from "having potential" to "career AHL player," so if he's not going to make the NHL roster, he needs to be traded to a team that will overvalue the eye-test things he does well (traditionally, the Buffalo Sabres have been that organization - but, maybe they're moving away from that now). We can only hope that the new management team has the numbers and knows what they mean, so that they can make the right decision now. I could definitely see another organization out there valuing him as an add-in to a larger trade, so if the new GM wants to try to acquire a 2C, Borgen is one of the guys who might end up part of that.
Personally, I like Borgen more than any of the fail-D drafted by the Botterill regime, and I would first be trying to divest my organization of guys like Samuelsson and Johnson before we get the inevitable visual and statistical confirmation that they're bad. But, I guess we'll see!