Mine die from time to time, I've had one completely lose leaves , stalk, everything, and I changed its soil, moved it outdoors into shade and it's come back great. I've discovered over the years before I grew it in Illinois before it became illegal it loves root room. Planting in the soil outdoors is the best for it. Indoors, you may get a season or three of heavy heavy growth and then death, at least in my experience. I keep them in pot s now and they always get sick over winter indoors S.A.D for salvia if you will. I've heard virus is associated as well but I'm not well versed with that. Mine are in room humidity and grow very slowly, but they re not pampered much at all, and seem happy this way, for winter. They do grow back from root well if...cared for properly. I think she likes respect, I alway took cuttings and harvested leaves when I wanted in the past and eventually I think she felt like a beast of burden and gave up. Now I take what she gives. And she is still here
So how to help you, if it is rooted, don't mess with cutting, reduce the humidity slowly over a few days, let the dead stalks harden and then cut off, if they are molding, cut them immediately, let the buds grow, but try to reduce humidity, very slowly, days. Watch your light, nothing too bright, behind blinds in a sun reaching window for a few hours plus a nice lamp near her and even temps, if the soil is always damp it s bad, at least for mine, let her dry a little, just a little then flood with rain collected water, I collect a few gallons if I can and save, ph is also key , but difficult for some, she likes slightly acid soil, rain water is perfect, mist with rain water if you have too, but I almost never, it's more of a treat while they winter indoors, the leaves will wilt and brown often, bad hair day, dunno, but her roots are strong and she always sends up pups . Wait till you can get her outside and find a decent high organic strong organic nitrogen based soil, I use chicken manure composted soil that's been mixed with hay that's been outside getting bio organisms into it for months before I use it in pots, but you could prob buy some cow or chicken bagged compost bags from anywhere mix with your yards soil , throw in some wheat or hay straw for moisture, let it sit in or on the ground to get the right guys renting rooms in it for your special lady. Then repot, put her in a shade lightly lit spot and hose her down from time to time. This is all the advise I can offer you, it's worked for me and believe me it breaks the heart when a cutting dies, but you move on and start another, eventually you get a beautiful lady pal, looking after you looking after her.
Oh and watch for bugs, certain white root eating bugs and white fly, again in my experience, are certain death, I take a tooth pic to small pots and stir the upper layer a few times over a few months, keeps them pissed and they move out