I'd prolly prune off the stems supporting the foliage that's obviously passed from this world. It's not a phoenix plant, so ther'll be no revival of those particular leaves. All you can do is wait and see if the heat (prolly not a light problem, technically speaking) damaged stem and root tissues so badly that the plant's on its way out.

Its water needs will have been significantly reduced, so be careful not to add over-watering to the list of obstacles the plant faces. It's a young plant, and young plants have a strong 'will to live'. I wouldn't write it off just yet, but be patient and don't forget it's on tree time, not people time.

Al

'tree time, not people time'

Good one Al, can I use that sometime?

Al to the rescue :>)

Lol - feel free. I know when I put myself on tree time, nothing seems to bother me. Working with trees that take me 3-10 years to get close to completing the vision I had for them (and probably changed at least a half dozen times) gives a whole new meaning to 'patience'. It's good for us to realize that some things just can't be hurried. ;-)

Al

I accidentally left mine outside (in Toronto) overnight. It looks like yours did. Did you have any chance with it? I’m so terribly sad :( I’ve had my tree for 8 years!

Nothing to do but wait ..... and avoid over-watering. Leaves are less resistant to chill injury than your FLF's woody parts, so there is some hope in that thought. Too, if the woody parts of the top also froze, it can come back from a bud/buds that break(s) low on the trunk in the immediate vicinity of the soil line.

Don't fertilize and be extra careful not to over-water. Your plant will use VERY little water if all the foliage is dead, and you don't want roots to be deprived of oxygen by a soggy soil. Give it a bright/sunny spot if possible. It can go outdoors, but only on days/nights when temps are 55* or higher.

Al

For clarity, it's safe to say that what's shown in the images is definitely not sunburn, though the point you make is a valid one.

Al