From 31st August 2010 to 31st August 2012, Sehwag has played 19 Test matches (Aus in Aus, Eng in Eng, RSA in RSA, and WI/NZ at home), and has averaged 37.26 with once century and 10 fifties.
His one century was a mammoth 173, which accounted for 13.65% of the 1267 runs he has scored in that time.
Not too shabby in itself. In India, however, he has averaged 55.25 and has scored his 1 century and 7 of his fifties.
This suggests that while he has be wayyyy below average in playing outside of India in the last 2 years (383 runs in 18 innings @ 21.27 with 3 fifties), selecting him for a series in India is completely justified.
Whether or not selecting him over a younger opener is best for India's long term interests however, is another issue.
The stats show that picking him for any of our upcoming away tours clearly is not justified, and he is bound to struggle. We may be better off with another (younger?) opener for those tours.
So if the long-term decision is that Sehwag is not going to tour with India, then it would be a wise move to drop him for the upcoming home tours and let a new younger opener (Mukund, Vijay, even Rahane) get used to the position on their home turf before exposing them overseas. As it stands, India could really stick almost any opener in India at the moment at the opening slot in overseas tours, and their not going to do much worse than Sehwag is at the moment.