Is it worth dropping 2 years to get into ISI Kolkata?

There is no doubt that ISI is an extremely and highly reputed institution. By any chance, if you are not left with any other alternative then it is worth waiting for ISI Kolkata.

• If you are planning for a master’s here, ISI Kolkata is a good choice.
• However, for a bachelor’s degree, you are advised to wait for a maximum of one year and not more than that under any circumstances. 
• It will be preferred if you go to other colleges.
• If you want to get a master's degree from ISI, I would recommend working throughout these two years while studying. 
• Do not just sit idle and do nothing as it doesn't look good on a resume. 
• Any work experience will be preferable to sitting at home.

If you are pursuing a bachelor's degree, study hard for one year, do nothing else, and ensure that you are accepted at the end of the year. Just to be safe, look into other colleges in India that specialize in mathematical sciences, such as CMI, Delhi School of Economics, IISc, and IIT.