The Rajya Sabha is a permanent body and unlike Lok Sabha, it will never be completely dissolved. Every alternative year 1/3rd of the members of the sabha will retire and new members will be elected by the electoral college as mentioned by the author. Every member will serve as a member there for 6 years. Some members will be nominated by the President of India based on the recommendations of his/her cabinet. The vice president of India will be the ex-officio Chairman of the Rajya Sabha.
What I feel is the remarks made by the PM on the eve of the retirement of 72 MPs are for the sake of courtesy and not that he really wants them only back again. He is not the person to decide who will come back. He may have a say in his own party but not in other parties. When some relatives come and leave while leaving we say please come again. This is courtesy. The same may be the case with the PM's remarks also.