are you sure the reviews will be lost?
According to the Google+ folks, yes, they would be lost.
I would if possible do a test with a fake account do a review delete and re add the page back. Then see if the review is lost.
We're actually talking about deleting the entire account, not just the page.
It's a good thought on trying a test with a fake account. I'll give that a try and let you know it goes.
In the meantime, here's a little more background on what we have done so far:
At one point I spent an hour and a half on the phone with Google+ support trying different things. One of them was creating a brand new page. G+ support said they could transfer the reviews after we had a known good, working page up.
So we stepped through the process with the G+ support checking it on their end at each step. The new page/listing had the same problem. I couldn't edit it from the dashboard. And the Google+ support tech couldn't edit it from his side either. And we hadn't even gotten to transferring the reviews.
So their current suggestion is to delete the page/listing AND the Google+ account. Any pages created under that user appear to have the problem. They can't tell me why.
And they seem sure that if we delete the user the reviews will go with it.
Still plugging away, but I think my client has just about given up and is considering starting from scratch, even if it means losing the reviews.