Sehwag going back home is not going to affect India at all. His form in the IPL was below average (but for that 1-2 innings at the fag end of the tournament). Also as sohum said (seems like I am agreeing with sohum a lot more today in many issues!), Sehwag is suspect against the moving ball big time and maybe he would have continued his bad form here in England.
So his absence wont hurt us. As scion_sid said, it eliminates the headache of whom to drop if he becomes fit and thats good.