I actually hope that US Sanctions India. But they did after their nuke test in 1998. And India managed. Things will get tough. But they'll manage.That's what you hope.
But Donald Trump has been going around calling India the "Tariff King". He has seen both the the effect of his words on the Indian Rupee as well as India's meek and basically non-existent response to the previous round of steel and aluminium tariffs.
If Donald Trump chooses to sanction India again for the Russia deal... then what?
India needs to sort out their currency crisis and deficit crisis ASAP.
Trump said before India's going to be his best ally. Not to mention he's actually friendly with Russia as well. USA may sanction India, but I think the possibility is quite low.