I am very sorry for your loss. A daughter and Mom have a special bond that cannot be broken, even when she is gone you willl feel her with you often.
As for your Dad, he needs time. He has had his soulmate and love for 41 years, you cannot expect that losing her will be easy for him to get over. But he WILL. And when he does how wonderful to think that he could find love again!
I think that you need to be accepting that if he does find someone special she will hopefully have something to offer you... not as a replacement to your Mom but as someone that can benefit from your Dad's caring nature and admiration and perhaps offer you friendship and guidance when you need it. Surely he still has more to give, he may find someone to share the rest of his life with but she will never take the special place in his heart that your Mom has always shared.
The incredible thing about love is just how much of it there is to give! We caregivers sometimes get so caught up in our spouses illness and the constant appointments and other matters that we forget how to live when they are gone.
Your parents may have discussed this. I have talked to my husband and told him that I would feel sadder to know that he did not open his heart up to someone that could give him the love I wished him to have and love my children as much as she loves him. (Of course I told him she cannot be prettier than me). There is so much for your Dad out there in the world. In time he will be ready to start.
In time, if he does find someone special, get to know her. She will be a companion to your Dad and, I deeply hope, a true friend to you.
To have a love that lasted 41 years is incredible... to think that he could find love again.. well, that is wonderous!
L.