I am diagnosed with a mitral valve stenosis, will i need a valve replacement heart surgery.?

Depends: This depends on how severe the stenosis is. It is important to see a cardiologist and continue to watch this condition closely as it changes over time, and you may need surgery at some point in time.

Maybe at some point: It depends on the degree of stenosis you have. If the blockage is high enough then you may need surgery. Unlike a leaking valve which most people get repaired - with stenosis many are replaced. It is harder to repair a blocked valve.