Well for starters, Apple was still selling the iPhone 4s in India until 4 months ago. Even in India, that's a pretty short window of support for a phone that was still pretty expensive by India's standards.
Second, the iPad 2 is still supported, and it was released 7 months BEFORE the 4s, and they have the exact same A5 processor and 512MB RAM, as well as the same graphics chip.
So all things considered, the 4s should be supported for at least one more year, whether it gets an upgrade path to iOS 10 or not.