Enligt VFS Global (det företag som hanterar Schengen-ansökningar för många konsulat i Indien):
What do I have to do if I have lost or misplaced my Indian passport with a valid Schengen visa?
You are strongly recommended to keep photocopies of your passport’s data pages and of the Schengen visa. A visa is a valuable document. Inform The Embassy / The Consulate from where your visa was issued immediately if you have lost your passport. You must apply for a new visa by submitting all documents and payment of visa fees. You must submit a copy of the Police First Incident Report (FIR) with your application. It is preferable to also submit a copy of the visa and the lost passport for ready reference of the Visa Officer.
Så svaret är att du ska ansöka om en ny visum med en polisrapport om ditt stulna pass.