Checkout Aditi Agrawal's reporting at HT, it was argued that WhatsApp as an App would loose its utility if it is allowed or to put it differently, eg legally india goes if anonymous posting is not allowed, it is the prime reason for its existence. Nothing was said suggesting that WhatsApp would leave India.
News 2- https://www.livemint.com/news/india/explained-why-is-whatsapp-challenging-indian-govts-order-over-privacy-11714101587758.html