I received the leaf from a reputable grower, and started it in water. Once it had roots, I planted it in a pot with african violet soil. For a long time, it stood firm and like a little soldier. Now it is limp, and I put a plastic baggie over it. Is it still viable?
The African Violet Society of Canada (link below) does not recommend starting cuttings in water. The roots created are weak and must completely re-establish when transferred to soil. This may be the cause of the wilt in your seedling. Don’t give up yet – give it a chance to recover. The plastic bag is a good idea but the bag should be only partially sealed. If the grower recommended this approach, I would certainly go back to them for further information.
You might find this link helpful: https://www.avsc.ca/propagation.htm