Formula: If cell 3 is blank have cell 1 calculate, if cell 3 filled have cell 2 calculate

Bare with me, I am not sure the best way to word this.

Currently column I(uncompleted) calculates days between current date and whichever date is later between columns E(Scheduled) and F(Arrived).
I would like column I(uncompleted) to continue doing this unless there is a date in column K(Notification).
Once there is a Date in column K(Notification) I would like column I(uncompleted) to become blank and then I would like column J(completed) to calculate days between column K(Notification) and the later date between Columns E(Scheduled) and F(Arrived).

Attached is an example that I hope will help you all to understand what I am wanting to do.

Let me know if you need more info to help clarify it more.