Another scenario came to my mind last night -
NDA couldn't manage to get last 5-10 seats to prove majority and BJP/Modi decide to seat in opposition rather then cave in to demands of 35 members of NDA, paving way for other Gathbandhan to form govt which would predictably fall within 1 year or so.
Ta Da. Re-election in 2020 for public to decide again on who forms govt!