welcome to Health care magic.
1.Very sorry for condition you are facing,
MRI is contraindicated with the metallic clips - first thing the clips can misplaced from location, second - metal will cause dirty shadowing.
2.Yes any metal in the body is contraindicated for scan.
3.CTA - computer
tomography angiogram would help in this case - presence of colt / blockage, narrowing. ( possible option)
4.A carotid doppler will help in sours of the
thrombus - Presence of any risk factors in the carotid and
vertebral vessels will narrow down the cause.
5.A good time based history will help in prefect diagnosis of
stroke and type.
Hope it helps you. Wish you a good health.
Anything to ask ? do not hesitate. Thank you.