Yes it is.
You did everything you could for your Dad. Often, those who seem unresponsive are more aware than we know. I'm sure you were a great comfort to him and, whether or not he was aware of anyone in the ICU, he loved you as much as you loved him.
If it is appropriate for you, you might talk to a spiritual advisor. Religions have been helping people cope with death for a very long time. If not, that's okay, too.