first- plumerias are not that disturbed by roots except when they are very young. As long as you did not tear the roots from the stem the plant should be ok. You may have just forced dormancy to set in. Plumies do not wake up until March-May. Leave it dry. No leaves=no water in case it needs to re-root. Mist the top. If nothing happens in 60 days you may have a problem. I generally do not transplant until the plant is well developed. A 6" seedling should have enough roots to handle transplanting. Also if all goes well, after about a year or more, use a knife to cut around the sides of the clay pot and don't use them any more unless glazed inside. The plants do not seem to grow as well in clay pots and the roots stick to the sides. anyway, relax and wait to see what happens. Plumies are usually dormant from nov-Jan to mar-may depending on location and weather. Bill

Thank You Bill!
I think the roots that were disturbed were more the very bottom ones. Funny you should mention it, because they were kind of sticking to the inside of the plastic pot as well. I had to use a little force to get it out.
I looked closely at my little trunk and I noticed a few Scale insects, which I hadn't seen during the transplant last month. I removed them, and it does look as though the very tip may have something in the works as far as future growth. The very tip is shiny- that gives me hope. I won't give up!!!
I may order some cuttings from Aloha Tropicals no matter what the outcome, just to have a few other varieties.
Should I overwinter my plumeria(s) in the basement next winter, at temps around 50- 60 degrees, or leave it in a sunny south-west facing window upstairs? (I live in CT)
Thanks Again!!!

Once the leaves are gone, the basement should be fine. Usually the black plastic pots are hard for the roots to stick to, but a long, thin bladed knife run around the pot before removing solves the problem. Also, if the tips are getting shiny, you are probably in good shape. Mist the tips. Watch for leaves to start. Bill

I am happy to say that my Plumeria is sprouting two leaves at the top- She Lives! I grew mine from seed, and it's been a slow process, but hopefully someday it will be worth the wait!

Seedlings can be a bit of a wait for flowers. I have some Cindy Moragne seedlings that bloomed the 3rd year and others that are 6 years old and 5 foot tall and have yet to bloom. Bill Moragne had one that took 20 years. Hope I do not have to wait that long. I would start a half dose of fertilizer now for your seedling and let it dry. Water and then water with fertilizer about two hours to a day later so the roots are not burned. Bill

I live in NJ and don't have a garage to winter my plumeria in. So this past winter I left mine in front of a window.

It had it rough... spider mites and partial dormancy.

but it made it and has come out of dormancy now and seems to be prospering.

My Plummie has three small leaves now- I have resumed watering and fertilizing. No more Scale, on this plant, anyway. Now there's an insect I despise. Delousing houseplants is a great way to spend some spare time! (LOL) I've started putting my plants out for a little fresh air and sunshine- Yeah!!!