URGENT: "legal non-conforming" triplex

[Andrew West]

BP friends & family! I would love some advice on a situation we've run into with a triplex I'm trying to purchase just outside Detroit (River Rouge, MI). I'm still learning the technicalities of this, so forgive any errors in my summary.

Essentially, everything has gone smoothly in our due diligence thus far and I'm told that our mortgage (conventional investment loan) is fully approved. We're a week before closing and some verbiage has been flagged in our appraisal by the bank that's underwriting the loan. It states as follows:

"Subject's use is legal non-conforming which means that if the subject is ever destroyed by a fire, it cannot be rebuilt as such."

As I understand it, this property was originally built as a single family before being sectioned off into the triplex it is today. At the time,  that was legal, but since the division, the zoning laws have changed to require only single-family in this area. The property has essentially been "grandfathered in" (hence the LEGAL, non-conforming), but if it ever needed to be rebuilt (in the event of a fire/total loss), it could only be rebuilt as a single-family. 

It's been a bit of a game of telephone as you might imagine from the underwriter, to the servicer, to me, but essentially I'm being told that this is a non-starter and they cannot close the loan. Specifically, they are honing in on the fact that it was appraised based off of being a triplex (and this is the value they are lending on), and that value cannot be guaranteed in the event of a total loss/rebuild, since it would need to be rebuilt as a SFR. I am told that this is a hard & fast fannie mae requirement.

I'd love to know from the community and any experts out there:

1) Is this right? any lenders familiar with this or have other investors experienced this?

2) Any creative solutions you can suggest? (we are starting to explore alternative financing with out team, and I'm trying to dig into the rules & regulations but I'm not a pro by any means)

The numbers on the deal are STELLAR and we'd hate for it to slip away if we can work or overcome this snag!

(final aside: I'm also being mindful that we may not want to end up with this property in our portfolio, and thus be stuck in the same situation down the road when trying to sell it)

THANKS IN ADVANCE!