Then sure. But that's what game theory is about. India announces that if China bombs Delhi, all options are on the table. China mulls over the potential ASAT

Then sure. But that's what game theory is about. India announces that if China bombs Delhi, all options are on the table. China mulls over the potential ASAT repercussions and decides the strike isn't worth it. That's the inherent safety of MAD. It requires no trust in your counterparty -- only convincing them that you will extract a heavy toll if (and only if!) they take a specific action.