Please do not think I am being judgemental as it is a tough subject, no one wants to lose their licence or job..and I understand that.
But and heres the big but.....you say he was lost did not know where he was, could he possibly get disorientated drive the wrong way down a one way street,? miss a red light,
You say he has had scrapes ? maybe your dad is worried too and does not know what to do, would it be best if you took the keys from him to safeguard him and others.
You say the nurse was made aware of this issue, this nurse is a professional and I believe it is her moral obligation at least or professional duty to report the concerns raised.
Your dad will take some time to recover from this loss of independance but if he killed or injured an innocent driver/passengers would he cope with the level of remorse, hurt in that scenario? Please give this some thought as it seems your dad poses a risk not only to himself, but other road users and pedestrians.
You could speak with the nurse so you have support and discuss this matter again. Should someone notify dvla of their concerns the dvla will investigate this including the reason why your dad continued to drive when it was obvious he was unfit to do so.
Good luck as this is a difficult for everyone involved, I think you may already know what you should do, be brave get support.