I'm pretty sure Amazon will let you return it within 30 days even without a warranty, make sure you read Amazon's return policy to see if that's the case, but if it fails 31 days or more after you buy it you are screwed
So it depends on if you are willing to take the chance, if nothing goes wrong you save $150, but if something does go wrong you lost $750
Personally I wouldn't take that chance, potentially losing $750 isnt worth saving $150 to me
I would either consider the extra $150 the price of the warranty, or if you're not willing to spend that much, get a 1070 for less
Also I don't know anything about buying things in India but $900 seems absurdly high to me ($750 is more reasonable but still too high), so I'd keep looking for a better price
As for future proofing, you'll get 4-6 good years out of either the 1070 or 1080, at 1080p the extra performance from the 1080 doesnt really matter since the 1070 can handle 1080p just fine, its when you step up to 1440p that you would notice the difference a couple years from now