I predict a strong 130-140 majority for the NDA, but low chance of them getting the 2/3rds majority needed for additional Rayja Sabha seats that they desperately need.
I also expect them to win in Bihar although not by a big margin. This victory and associated Rajya Sabha seats are very important for Modi since a comprehensive victory here will kickstart the reform process stalled by congress and stooges.
A weak showing on the other hand shall slow down the reforms and make passage of essential bills like Land acquisition, labour reforms virtually impossible to implement and that will reflect in 2019 when country goes to poll.
Modi will have less to show and talk about and thats what the opposition is counting on.
Modi also knows this and hence the reason he has gone full steam on bihar. He has to win this at any cost.