According to Bob Cain, NMSU Extension Forest Entomologist, the blackening of the bark could be due to sooty mold, a fungus that grows on the honeydew excreted by aphids, white flies, or other sucking insects which have been feeding on leaves in the tree. However, sooty mold should not cause the bark to die and peel from the wood. There may be sun scald damage to the tree occurring in the winter caused by the bark heating too much in the day when there are no leaves to shade the trunk. It may also be possible that there is a vascular disease active in the trunk of the tree causing the problem. Another possibility is that there are borers infesting the trunk.
Borers are quick to attack trees damaged by other factors.
It would be a good idea to contact your local Cooperative Extension Service office, a free service of New Mexico State University. The Extension Agent can often diagnose such problems and give an immediate recommendation. There is an Extension Service office in each county, so there is one near you. There are also volunteer Master Gardeners associated with the Cooperative Extension Service who can be of assistance. I am not sure if you are asking me how long an African violet flower lasts, or how long the plant lasts.