Trending @Accenture; How to force manager to give roll off ?

The only correct solution to this is to speak up. Even if the project has dependency on you doesn't mean you need to work here till the rest of your life. Approach your supervisor with a very high valid reason on why you need rolloff. Most Important keep all this documented in mail.

How many earned leaves do you have?

They won't give roll off and will state reasons like we haven't found your replacement and pretend to show that they will release you when then they find someone.It's better to search outside , your frustrations won't matter to them