OK so I understand properly...

1. we are talking about col B, correct? And in particular, B7

2. If A6 = Yes or NA, B7 = ""

3. If A6 = No, B7 = Complete

4. But if A6 = NO and C7 contains anything, B7 = "" (shows nothing)

Am I understanding you correctly?

The best way to prevent accidental deleting is to protect the cell/s