Firstly, Ishaana has always been one of my favourite characters (second only to Rudra) and I have been mighty disappointed with her extended absence on the show. In any case, I am more than willing to be patient if the writers give Ishaana a purposeful return and consequently, a proper, and more engaging story line. Though, knowing what we know about the writers, there is no guarantee of this.
As per spoilers, the Oberoi youth will soon discover Gayatri's motive for targeting their family as well as become aware of the dangerous nature of the age-old secret that Tej and Shakti have buried.
Since it is obvious that neither Tej or Shakti will confess to the secret, I would like to see Shivaay hire Ishaana to uncover what they are trying to hide.
Ishaana is an awful con-woman, but she is an excellent researcher and a skilled thief. She is able to find out about the Maha-Aarti incident, even though no media outlet was allowed to broadcast the news. Ishaana would be industrious at corporate espionage and that is exactly why Shivaay should employ her, to dig through their company history and the shady past of the senior Oberoi brothers.
Besides, I would think that Shivaay would hire someone already with intimate knowledge of his family affairs, rather than a PI, because he would not want anymore people to become privy to the skeletons in their closet.
From here, I can see the IshKara story progressing from an intense mutual hatred to slow understanding. But of course, it could later feed into much more drama if, according to many viewer predictions, Ishaana is actually Annika's sister and their family was the one that the Oberois destroyed.
Now there would be some great irony and more importantly - angst.