Is my Ficus Fusion Project Dying?

The tree as it looks today (front view)

Everything was going so well with the Fusion Project which I've been developing from a bunch of Ficus Natalensis cuttings over the last four and a half years.

I was finally happy with the way the trunk was fusing and had started some styling work.

In the period up to January 2020 I took it to a couple of meetings looking for advice.

January 2020 - before pruning

A few people felt that the first branch (the thick one, above the cutting I've planted to try to widen the trunk) should be removed, but I didn't like that idea and chose to shorten it instead. I also felt the tree was getting rather top heavy, so I cut it back to a new leader.

January 2020 - after pruning

For a while everything seemed fine but the first signs of trouble appeared sometime in March, shortly before lockdown. I have a photo showing serious die-back which was taken on 27 March. That was the day I decided to remove the dead leaves, but leave the branches intact in case some of them survived.

At the time I thought that a badly executed cut had killed the top and I wasn't too concerned about it as the tree was taller than I wanted it to be anyway. I was unaware of any further problems after that.

A couple of weeks ago, when the first signs of winter appeared, I moved the tree into my greenhouse.

Then this morning, I noticed a whole new section of dying leaves.

Best case scenario here is that I'm going to have a much shorter tree than I'd planned. To be honest I'd be quite happy with that.

But right now I'm terrified that this is just the beginning of the problem and that the tree is dying. And right now, with the Covid-19 pandemic in full swing, I'm unable to take the tree anywhere to ask for advice.

If anyone reading this can offer me some assistance, it will be most welcome. I've put a lot of effort into creating this tree and I'd hate to lose it.

The tree as it looks today (back view)