What is the progonsis for a person aged 49 years with severe small vessel ischemia?

Do you mean brain?: Might need to ask a neurologist this one. Small vessel changes on the brain may or may not be significant for the possibility of vascular dementia but may also be age related. Best to seek medical evaluation here and undergo some sort of memory assessment. This will help work out whether there is an issue or not. Your GP should be able to start the ball rolling here with a memory test

Microvascular ds: Coronary microvascular disease describes poor oxygen supply to the heart despite normal major arteries; the idea is that the tiny blood vessels don't allow normal flow. It is often discussed but is hard to diagnose. In my experience most people given this diagnosis don’t actually have it. Since you have had evaluation, it may be worth getting a 2nd opinion; consider a HealthTap inbox consult.