If you graduate from IISc and decide not to pursue Phd, then organizations like ISRO, BARC, CSIR, DRDO, HAL, CEERI, TIFR and other R&D government organizations will definitely pick you up. Apart from that there are many R&D private companies like Hindustan Lever, IBM, Microsoft, Google, Biocon, etc.
There is a lot of scope for jobs outside India like Germany, USA and other European countries where R&D is given much more importance than in India.
IISc is very well known outside India and the tagname of IISc will help you getting a good job.
After doing Phd (which becomes easy once you graduate from IISc), the academic line is also opened for you.
Some people may say that job prospects after graduating from IISc are not very good but I can't believe that a graduate from the institute which is best ranked in India can't manage to get a well paying job

all the best

Hello , 

You are taken by iisc as a research scientist. You can join private companies for research jobs . There are many more opportunities than these.