SWIM has a few small Psychotria viridis which he has managed to grow from seed. He's in the southern hemisphere and the plants have been doing great all summer. He has them in a makeshift hot house by the window and there is a heat mat under the plants as well as an ultrasonic humidifier too.

Recently the leaves started turning a little brown and have started to wilt at the ends, and they feel kind of dry when he touches them.

SWIM re-potted them earlier into fresh medium made up of cactus compost, organic potting mix, and perlite 3:3:2. SWIM read about "root rot" and was worried that perhaps with lower temperatures here lately, soil moisture was buidling up in the pots?? SWIM could be wrong.

He's worried that they are not going to survive the winter. Anyone have any tips I can pass on to him??

Any help to revive these little fellas would be greatly recieved

Thanking you all in advance

Ya looks like root rot, maybe too much water, this plants like water but may be you give them a lot water, keep them humid by spraying water on them and don't leave the heat mat on all the time, adjust the timer to work for 15 minutes every 30 minute

Thanks man!! Do you think they are salvagable??

IMO they look more than salvageable. I def agree that a constant heat mat can also be a problem possibly the problem if you aren't over watering. If you have been keeping the soil too moist and its very moist now you may want to gently re pot them in new soil and a bigger pot.
Try not to disturb the root ball too much, even more dry soil around the root ball will draw moisture away from the roots and not shock the plant too much.

Just a suggestion, you will know best. But if you do have root rot, and the environment is somewhat humid the plant will not be taking up water in the damaged roots and the soil wont dry out in time to save them. That's why I suggest possibly re potting and certainly turn the heating mat on a cycle. Take a temp reading of the soil when the mat is on. This can also help you understand whats going on.
Chacruna is a hearty plant and can take a beating such as its natural environment of the rain forest, if the roots are healthy.

Thanks Olympus. Positive vibes for these plants.

SWIM repotted them already into new soil. Cactus mix : Organic compost : Perlite 3:3:2. He sat the plants on a polystytrene block about 2 inches above the heat mat. He's spraying them with a low concentration micronutrient fertilizer twice a day. The largest plant had a new set of leaves coming through just as it started to decline. Hopefully this new set of leaves will emerge and be nice and green.

Thanks for the tips. Any more you have are most welcome