Sounds like China part II, but potentially even worse long-term given the lack of a tradition of unity in India unlike China. After all, no one's ever united all of India (let's assume the modern Republic of India, give or take remote regions like Manipur, as well as Bangladesh and as much of Pakistan as possible). The Mughals came closest, though the Maurya were also pretty close albeit they had nice holdings elsewhere, so this Hindu empire would be the first.
Also, wasn't the ruling of India insanely decentralised? That would make it even easier for Western powers to carve concessions out of the place. The good news is, if this Indian Empire has centuries of unity, it could in theory reform using some nature of Hindu nationalism. What that means for Muslims, probably not good. And if it does fall apart, there could emerge movements to put India back together, no doubt involving particularly bloody civil wars (and of course mass famine on the levels of the worst of British India, if not worse).
United India would have higher development than British India, and probably slightly more population (consider the relative stagnancy of British India's population compared to other places globally in the same era). There's potential for some level of industry in places like Bengal, assuming some skilled leadership.
The impact on colonialism in Asia is going to be ridiculous, and to a lesser extent, European colonialism in general. While Europeans might be able to seize entire regions like the British did with Bengal, we should assume from this scenario that that is by no means inevitable, meaning Europeans will have to be content with a China-like network of small concessions. Oh, and also expect Europeans to own massive amounts of Indian capital, like the railroads, the mining. If India slips up for a second, then Europeans will basically indirectly colonise India, and could easily splinter off regions of it into more pliable states.