Employer asking to work till notice period with money

Sir, I am working for a software company as a programmer and joined 16 months back, and about to complete 18 months by December 28th, 2017, which is mentioned as in the agreement. My employer quoted termination clause typically in their favour, like, If employee want relieve from the employment within notice period (3 months) then have to pay an amount equivalent to the Package agreed (for ex: 10,00,000/- p.a. package). Is this justifiable even if signed with them.? Can we defend if they demand to pay that huge amount.? If they bargain it to 250000/-, can that be payable without any ground? Now I got on opportunity with a company out side India, the same is been informed to them hoping that our employer agrees to relieve me in as this offer is for outside country. I expressed this a month ago, even now they kept me pending and threatening in such a way that, they stop my abroad trip by complaining with Embassy / employer as about absconding. After the above discussion, I told them to work even from outside country till Dec 2017, else I also given an option that, I will l pay 3 months of basic salary. They are taking advantage of my sincerity in disclosing the new employment outside country India. Can they stop my fly to outside country, which is planned this weekend.? What consequences I should face if they proceed legally against me? Please suggest the best option to take.