Welcome. Jan.I think every grief is different and its a bit of a shock when the pattern you accept goes with it changes.Guilt is very common though,what if I did or said something different,but if you try and turn it round you will often find that the alternative option might also have created a reason to feel guilty too,in a way.I don't know the whole of it but it could even be that your dad chose to slip away when you left the room,as a parent none of us want to put our kids through more pain than they have to experience and rightly or wrongly make the decision purely through love.I am certain my mum did that,and knowing I wasn't going to leave perhaps my husband waited until other family members arrived so I would have support.I don't know but that's what I feel.
I was determined my grandchildren would remember their grandad a couple were very young and three born since then.But I have heard the older one telling the young ones about him,so he does live on in that way.