All the leaves fell off of my seedling that I got from Mimosa nursery. It has been in the ground since spring of 2016. Its about 2.5 feet tall...trunk is about the thickness of a quarter. I scratched the skin by the trunk and it was dark brown... but I scratched the skin of the branches at the top of the tree and it was green. I am assuming that it is still alive and didn't die since the branches up top are still green under the skin. Also, I have it planted about 5 feet from a south facing wall so it does not receive any sun throughout this whole time...it is in the shade. In the summer it gets full sun.
It may be very well dead from the ground up. That's what happened to one of my Sweet Tart mangoes I planted on my parent's ranch. I had plastic surrounding the tree, but a wind blew the plastic over during or after the heavy rains. I have been busy, and hadn't been over there in like 3 weeks. So with the plastic sitting on top of it, it stayed in a super humid environment sitting in cold soggy roots for too long, and it died from the ground up. The top of the tree was green under the bark, but it was dead at the trunk when I found it in this condition. Now it's completely dead.
It was in filtered sunlight so I know it wasn't greenhouse induced heat damage.
On a side note, I had 2 in-ground 2 foot soursop seedlings underneath a tree that lost all its leaves during the winter. It got down to 27 degrees and killed one for sure. But it looks like one of the 2 is growing back. I'm surprised on how tough some of these subtropicals are. The cold got the one soursop, all the papayas, and one sapodilla (I thought they were tough?). But all the mangoes, except the one mentioned, came through like a champ. Even the tropical guavas all survived and are rapidly growing back leaves.