Hello Ajaya,
There is no provision for this. There are 3 options seen to me option for technical solution.
1. Find suitable ImplicitEnhancement point in program SAPLIQS0 to put a code which prevents the Task Deletion
2. Modify the Tasks screen Module pool program to make this icon invisible in your Notification type again through ImplicitEnhancement.
3. Creative use of user-exit QQMA0014, using field symbols, to retrieve how many lines are there in Tasks table (QMSM) for this Notification, and how many lines are there now at the time of Saving the Notification and accordingly throwing an error message which stops Notification Saving.
Show this to your ABAPer. He might come with a solution for you.
Another option in standard, often people suggest in such situation is a Transaction variant (for IW22) through SHD0, which might have some difficulties.
Good luck
KJogeswaraRao