I agree with bjp's judgement/calculation...
bjp will potentially lose some muslim and hard core secularist vote.. but they never voted for bjp anyway..
by fielding modi, bjp will try to create a hawa (its already doing.. and congress is inadvertently helping by going after modi in big way)... so some fence sitters will support bjp (those who usually vote local party) and those who are not hardcore congressi ideologically.
however if Modi does not deliver the number (NDA falls short of expected number of seat), he will be withdrawn as PM to attract other parties... this will be during post poll horse trading phase..