I have a small key lime seedling that was growing pretty well and I decided to repot into a slightly larger container, but I screwed up and didn't remove the old soil. My new soil is a much better draining mix that I've used with pretty good success for my meyer, but as I'm sure you've guessed, the seedling has started to fade. It has quite a bit of leaf curl so I removed it from the container and saw the old root system encased in pretty wet soil and some of the roots looked pretty bad. This morning, I did what I should have done to start with and removed all of the old mix, cut away some of the roots that looked bad and repotted in the fast draining mix.

I have about 20 newer seedlings that look great and are much healthier thanks to what I've learned here so it's not a huge loss if this one can't be saved but I'm curious what you think.

As long as the roots weren't damaged too badly it should recover in time.

Also don't forget some of the roots have died away, so perhaps the ones that are left are struggling to maintain the foliage. They may just need some time to expand so they can support the leaves again. I'd withhold from fertilizing if possible and just give it some good light and time

Just to add, as I can't tell from the pic, seedlings need moving air - whether they go outside or have a fan in the room to make them twitch. This is what helps them build stronger stems. You probably already know that, just making sure