The scenario that you have mentioned is perfectly plausible. However the following should also be noted.
The kidnapper should be sharp enough to get your mobile phone as well. So in your case, keep one phone where you get the OTP with your family or at home and when you walk around use another phone. Without OTP the kidnappers cannot do the transfer.
When you are getting tortured, do lie about the password as after three attempts the online system will be blocked. They may think, in nervousness you gave them a wrong password. The downside is you will be tortured more.
With regard to trading account withdrawal, not sure if Zerodha would be concerned, but when large sums of money, (If I guess right per day RTGS limit is around 15lack), this will give sleepless night to your Bank RM and he might try to reach you or call you. Be friendly with him so that he will notice the withdrawal
I am sure your family, or friends or someone whom you owe money will miss you and they might report you to the police. So be nice to family and friends. Tell them that in case you go missing after reporting to police, go to the bank and ask them to freeze your account. Write a letter and keep it with them.
On a serious note, these kind of paranoia is natural with few people. It might be fun to read and even more easy for writers like me to make a joke, (apologies, but I just could not resist) but do consult your doctor. Few people cannot travel in AC train in India because of the dark tinting on the windows (now I heard it is better as the window glasses are lighter) and it becomes worst in the night. Claustrophobia.
I know a friend of mine who opens FD at the branch manually and not online as she feared that if her account was hacked, the hacker cannot close her FD online.
So if you have this persistent paranoia and if you dont need so much float money in your account, and if you are a trader, you could place the float money in mutual fund and pledge it. (Not an expert on this aspect but have read many traders doing this).
Disclaimer: My apologies if the above is offensive, but do take it on a lighter note. I am sure nothing of this sort will ever happen. Dont focus too much on this aspect.