It can be fatal, depending on the cause.
Vasculitis in dogs can be fatal if it goes untreated for a long time, but vasculitis typically responds well to treatment and most dogs make full recoveries. (see vasculitis symptoms above)
For example, cutaneous vasculitis in dogs is usually seen on the skins and fur of dogs.
This is a very obvious sign of possible vasculitis (because it's on the skin, somewhere we can see).
If caught early, can be properly examined to determine the root cause of the cutaneous vasculitis (even if the actual problem is beyond skin deep)