It seems pretty straightforward to me that an Islamic conversion of most or all of Christian Europe would do very nicely; then Islam can suffer all sorts of setbacks and barriers in India and still come out ahead.
It's a chestnut going back to Toynbee (writing in the 1920s IIRC, one of the earliest volumes of A Study of History) that one mode of failure for Christendom could be that the Norsemen decide they'd rather convert to Islam than Christianity. Or maybe Toynbee never said that; he did IIRC suggest though that Islam could prevail on most of the Continent, with Christianity holding out only in its Celtic form in Ireland and perhaps the British Isles as a whole, with the Vikings going for Celtic Christianity. So that would preserve some Christendom, in another form Toynbee thought would be more culturally compatible with Islam.
So 1000 AD may be too late for that particular scenario.
Anyway I don't understand the assumption that Islam can't simply triumph in Europe; that would certainly put it over the top demographically.
And once Europe is Muslim, why wouldn't we want Europeans to be the ones to expand into the Americas? That would just tip the balance even further in Islam's favor, no matter how poorly they do east of Persia. Leaving plenty of room for Buddhism and Hinduism in India itself plus any territory to the east or southwest they can stake out.
Totally wiping out European Christendom (by gradual conversion over centuries, not by any more violent means!) would certainly open up second place for the Indian religions even if they do lose a lot of ground to Islam.
So, why not? By 1100 AD it might be too late for the Muslims to prevail, but it isn't clear to me 1000 AD is. The Vikings were still raiding then, creating all kinds of mayhem; I forget if the Magyar disruption of central Europe was at that exact same time. So if the Magyars are already Muslim, and the Vikings decide it's the wave of the future and it spites those Christians who have been nagging them for several centuries now, and some misstep in Aquitaine or especial effort from Muslim Iberia moves Islam north into France, the overall collapse of Roman Catholicism might be at hand before that century is out. Then it would be a matter of mopping up Italy and Germany and the Lowlands; Britain might hold out for a while or go under eventually so as not to be isolated.
I certainly can't offer a specific POD--but why this assumption Europe would be immune?