Ornamental purple-leaf plums (Prunus cerasifera) are relatively short-lived trees, with a couple of decades being considered a reasonable lifespan before they tend to decline in health and/or appearance. Reinvigoration tactics are usually not worth the effort and likely won't be successful, so replacement of this tree is a worthy consideration. Causes of dieback and decline are numerous with this species, and can include pathogens causing cankers and wood-boring insects, both of which can damage sapwood, cutting-off water and nutrient supplies to branches or foliage and resulting in wilting and death. Neither is treatable once symptoms manifest. Plums, like their cherry relatives, are also sensitive to excessive wetness in their root zones, such as from over-watering, poor drainage from soil compaction, or temporary flooding from downspout outlets or other sources in wetter-than-average seasons.

For now, if you are keeping the tree, you will likely need to prune out all branches with wilted growth. While frost damage can cause similar wilted and "burnt" symptoms, and many areas have experienced colder-than-average nighttime lows recently, frost-affected branches will leaf back out in the next couple of weeks, while dying branches will not.

The pale gray/white spots on the bark are harmless lichen. While they can grow on just about any surface, including on perfectly healthy trees, they tend to become more prominent on declining trees with sparser canopies, since more light reaches their bark and allows the lichen to photosynthesize more. This by itself does not need any intervention.

Miri

You're welcome!