I've grown many F. Benjamen over the years and have not had this
problem, not even a little leaf drop which rather surprised me.
However, I summer my trees out doors in a bright area on my patio, but
without direct sun. They winter indoors in the basement light garden,

My basement stays rather cool (60*f.) during the winter, I do cut way
back on watering, allowing the soil to become dry to the touch between
water applications.

Your tree's problem is in having kept it too cool. They do not do well
in temperatures below 55 degrees, remember this IS a tropical plant.

You've already moved it to a warmer location and this will help, if it
isn't too late. DO NOT WATER the plant until it shows new growth,
unless the potting mix becomes completely dried out. Keeping it too
wet in it's current state would be a death sentence for sure. And
definitely DO NOT fertilize it. In fact, NEVER fertilize an ailing
plant. Period.

I am currently down to two "Weeping Figs" that were potted together in
a 14 inch pot several years ago. They have doubled in size in the last
four years, and that would be more if I didn't keep them pruned. The
last two of my bigger trees had to be given away because they just got
too tall for the space I had for them during the winter months and
pruning them down to size would have ruined them.

I have grown several different tropical trees for years by being able
to put them out doors during the growing months (June to September in
my zone), I have one Tropical Hibiscus that is 20 years old and still
going strong. It was started from a semi-hardwood cutting and stands 4
feet tall and 3 feet wide and I maintain this size through careful
pruning every Spring.

All of my "house trees" get the same winter treatment in that they all
must go into the basement light garden and grown cool (but not cold)
and somewhat dry.

I would not re-pot the ailing ficus at this time. If it recovers, I
strongly suggest you do some judicious pruning to get it back into a
pleasing shape. Many of the smaller twigs will die back and there
could be some die back on the larger branches; once the tree is well on
it's way to recovery (usually within a couple of weeks) you can start
removing the dead areas. When the tree have fully recovered you can
re-pot it to the next larger size pot. Although what you will probably
find is that the plant suffered serious root loss from being kept too
cold. In this case I suggest doing some careful root pruning and
returning the plant to the same size pot.

Hemmaholic