apple watch 9 Blood Oxygen Sensor

If you bought one that has the feature disabled from the US taking it to another country does not change that. You would need to either purchase one from outside of the US or purchase one at an authorized US retailer (not Apple) that still has inventory of the watches that do not have the affected part numbers ending in LW/A. Best Buy for example is an authorized Apple retailer that still has inventory with the feature still working.

The last part you asked no one can answer. Until the lawsuit is resolved or settled you won’t hear any official statement from Apple about what will or won’t happen with the watches that has the disabled feature. Anyone claiming to know definitively that it will or won’t be reinstated is guessing and therefore not a reliable source of information on this.

No.

About Blood Oxygen availability - Apple Support

If you do not buy a U.S. Series 9, then the O2 sensor will work.

I assumed this was yet another post about buying an Apple Watch in the U.S. and taking it to India. We get a lot (really a lot) of posts about using a U.S. Apple Watch in India. Mostly those are about will the cellular service work.