Can nerve irritation like sciatica or pinched nerve in the neck lead to stroke, if pinch is long lasting?

No. Stroke occurs as a result of an insult to the brain. Typically due to lack of blood supply to a portion of the brain, which occurs following a bleed or following a blockage of arterial flow to the brain tissue. It does not occur due to nerve irritation from a "pinched" nerve.
No. Stroke occurs in the brain. Sciatica refers to irritation of nerves originating in the spinal cord.