Do not let all of those branches grow from a single spot - remove all but the most vigorous of the clump - and stay after it, or you'll end up with a huge and ugly swelling.

That it's growing back so vigorously from the base makes me suspect the top's a goner ....... but do do the scratch test to check the top's viability.

Al

The tree asking you to leave it alone.. lol. This tree try to survive by making closest route to do normal metabolism so it grew buds on base of the trunk. The upper part of the tree maybe still alive, but only if the energy by photosynthesis sufficient enough then upper part of the tree will grow, so just leave it alone for a while.. It's new root still weak.. or might not grow at all, yet..

There is only one degree of dead. The top is dead ...... or it isn't. The apex of the tree is a stronger energy sink than the bole, which is why the top and branch tips are the first to respond with new growth after a tree is defoliated. If the top is no longer viable, the point is moot. Also, the leaves on the current flush of branches are net USERS of energy until they are about 75% mature, only then do they make a net energy contribution over and above the break-even point; so at this point, the new leaves are drawing primarily on energy reserves stored in roots and cambial tissues, not on current photosynthate.

Al

Thanks tapla, I will go with your recommendation, see images below.
Also, I am showing all photos to get better understanding of where she is coming from.

Before repotting she was loosing significant foliage:

I was assuming it was due to small container and overcrowded roots:

Soil was rock solid and compacted between roots. Even with continuous water showering it was a tedious task to remove old soil. In order to do so I had to sacrifice some roots. Also did some additional pruning to get rid of overlapping and crowded roots:

And placed in larger container:

Leafs continued to fall, so I cut of the dead branches. Then cut off even more. I assume this was the big mistake.

The remaining leafs fell too.

New leafs at bottom

Selected most vigorous one as per Al's recommendation:

Scratch Test. Checket at various heights, although showing where green suddenly looses color and turns into pale brown (surface here is wrinkled and feels mushy beneath).

So this is where I am now. I understand I did some serious mistakes, and I am open to harsh criticism so please tell me where I was wrong about repotting.

And most importantly how do I proceed?

Many thanks!

It's too early on selecting brances. Every leaves important for photosynthesis and create energy for the plant. Wait till lil bit woody..., beside for ficus, you always have chance to join multiple branches to create one big branch.

Now take care of that single shoot more carefully. Don't let human, animal, or desease break it.

All you can do now is wait and make sure you don't over-water. Keep it warm and give it lots of light. Definitely move it outdoors when temps allow. It will take full sun, but keep it in open or dappled shade until it starts to come around.

You didn't make a 'mistake' by eliminating all but the most vigorous branch. The tree will invest as much energy in the single branch as it was investing in the clump of branches you removed. Had you not cleaned up the cluster of branches, you would have ended up with a huge and ugly swelling at the base of the cluster. Depending on whether or not the trunk is still viable above the low branch you have now and back-buds, you might be forced to create a new tree from the branch you saved.

Approach grafting of several branches to each other in the hope that inosculation eventually occurs isn't likely to yield a result you could expect to be eye-appealing, especially if it's your first go-round at it.

These are Ficus B, approach grafted, inosculation fairly well underway:

Al

Thanks Al.

When you say place outside under direct sunlight do you mean exposed to rain or under shading structure?

Regarding grafting: I am fine with going with just one branch. So I was thinking... Would it be possible to graft new branch to old trunk? Does old trunk have to be alive? It would be nice if new branch could "climb" to top of old trunk and branch off from there. As in my sketch below. Any ideas how to achieve this?

In bonsai, grafts to old wood or dead wood are common and what you're describing. The name of the style is "Tanuki", a reference to a shape-shifting monster found only in Japan's folklore and not under beds. There IS a canine that makes Japan home and looks like a cross between a dog and a raccoon that is also referenced by the same moniker, but knowing what I know about bonsai, "Tanuki" references the shape shifter. Here in the USA and in Europe, it's more often called a Phoenix graft. You can certainly use the stump to make one if you like. They're easy to perform - not as easy to make them look natural. Most often they are made by carving an indentation in the host tree, then the live branch is trained to grow in the groove. In about an equal number of cases, the tree is either tied/zip-tied in place, or brass nails are driven through the living part into the deadwood. Don't over-drive the nails and mash your living branch, or you might get to meet Tanuki first hand.

Careful - I didn't say "Place the tree in direct sun, "I said it WILL TAKE direct sun, but, keep it in open or dappled shade until it comes around". Your tree's energy reserves are very low, so you should avoid the potential for sunburn by keeping it in open/dappled shade. Open shade is is shade with open sky above it. In the N hemisphere, that would be shade on the N side of a building, fence, ......., just so the sky above is open. Open shade is brighter o/a than even dappled shade.

To achieve it, You can press the tree against the trunk and wrap it tight with grafting tape, wet raffia, veterinarian wrap (what I use), jute/burlap ribbon. If you can salvage the leaves, include them in your composition. They will foster branches and help the trunk thicken and the graft 'take' much faster.

Al

Tanuki is common for conifers and pine deadwood, but not for ficus. Ficus deadwood will become soft like sponge and turn to powder easily even if you apply lime sulfur to prevent it to happen. That's why jin and shari (carving deadwood method) isn't applied to ficus bonsai.

If you wanna grow that tree, first thing to do is, let the tree grow it's root without too much intervention. Let all branches and leaves grow for at least a year. You can zeroing all branches and start do design after the root strong and healthy.

Or.. if u want instant result, buy small ficus, find appropriate big deadwood with good trunk movement, then start making tanuki.. even tanuki isn't common for ficus bonsai for some reasons, for houseplant it might be still nice to see.