I'm a huge fan of Office 365 products and services but I have to agree with the large majority of people posting that this is a huge backward step for us. People who use OneNote heavily, the proper desktop version not the useless online and Windows app versions, will not have the functions that they rely on to do their job effectively. OneNote has been my secret weapon of choice for more years than I care to remember. Ive got day notes and planning notes going back over a decade.
I know you won't reconsider and change your minds over this awful and frankly stupid decision, the marketing people are taking over again and forcing you to do this. However as a result I will, and with real sadness, have to look for alternatives for integrated note and task management outside of the Microsoft products.