Honestly, I'm very sad hearing this news. I really liked Saurabh. He was a very good and loyal friend to Anirudh.
However, I have always felt that Saurabh hardly had much of a role to play in the show. His character was too meek right from the beginning. And it is possible that the actor playing the role wasn't very satisfied and felt the character didn't have much scope. It's just my assumption. Dev is a pretty good actor and it was evident from they way he portrayed Nawab-e-Tulsania. He even seemed very happy playing that role and also received a lot of praise for playing the Nawab. It's just possible that like Pallavi he too wants to branch out and do something different hence the PH took the decision to bring the widow track. I hope they do justice to it. Honestly, I always thought they would use Sumati to show the widow remarriage track.
P.S. This is all just my assumption. It's also possible that maybe it was planned from the beginning.