Will Indonesia become 2 countries in the future, West Muslim and East non-Muslim?

 Such division does not exist in Indonesia, Indonesian diversity is not limited to west is Muslim or east is Christian like Malaysian, Thai and Filipino case where in eastern Malaysia (Sabah and Sarawak) has concentrated Christian population, south Thailand (Yala, Pattani and Narathiwat) has Muslim population or south Philippines (Mindanao) has pocket of clustered Muslim tribes.

Ethnic Batak of North Sumatra

In Sumatra, where the Malay people have long intertwined history with Islam which brought by Arab traders, there's ethnic Batak from north Sumatra and their sub-ethnics with huge population of Protestant followers spread all over Indonesia.

Even so the Malay people from south Sumatra still have strong roots of the Buddhist Sri Vijaya Empire which based in Palembang.

Malay of South Sumatra

In Borneo/Kalimantan, central Indonesia we also have numerous indigenous people under the same umbrella term 'Dayaks’ who are mostly following Christianity and other native faiths.

Dayak people

The Javanese as the majority ethnic group in Indonesia have culture which still has strong remnants of animism, Hindu and interesting historical twist with Islam.

Depiction of Javanese king Sultan Agung

So while eastern Indonesia arguably accepted Christianity massively than any other regions in Indonesia but they still have successive sultanates which don't fit to this west is Islam/east is Christian narrative.

Sultan of Ternate, north Moluccas.

Balinese costumes

Also don't forget that Bali is and always predominantly Hindu which located in central Indonesia and often being called as the gate to know Indonesian culture in entirety.