--there doesn't seem to be a good expression for such a thing--
if i said "my condolences on the loss of your father"--that wouldn't be accurate because i don't believe you have lost him except in the physical sense.
i believe those who have "passed on" have "passed on" or "crossed over" to another dimension and they are able to continue to see us/be with us/hear us. i don't believe they miss us at all because they are still around us.
some people pray for their loved ones--i believe we can still talk to them and that they can, and do, hear us. they listen, they watch, they "whisper" to us (even if we don't consciously hear them) and try to help us and communicate messages to us.
i believe they give us signs in order to communicate with us when we ask for them and even when we don't ask. with my mom--for the first number of months--i didn't think to ask for signs--all i could think of was "she's gone, she's gone, she's gone!" i was so bereft. and my mother was probably thinking "i'm still here! pay attention!"
and in my private hysterics one time there was a loud bang on the outside of the house which snapped me out of it. i went outside to see what had hit the side of the house. there was nothing there.
another time i was sobbing and i heard a crash in my daughter's bedroom. my daughter had gone back to college three days before and her door was closed. the sound snapped me out of my hysterical state and i went to investigate, finding a heavy container had fallen off a footstool in her room.
and the first time i sat down to read anything (about five months after my mom "left" i was reading the book "we don't die" when the light flashed on and off at the same time there was a knocking sound on the wall behind the couch--this was done in a pattern of two knocks and then five with the light flashing off and on each time. when i realized i hadn't blown a fuse it occurred to me that the knocking was the reverse of a "signal" we used for each other (the "shave and a haircut--two bits) which my mom and i used to let each other know it was us on the other side of a door. and on the other side of the wall where the knocking came from was my mom's bedroom.
definitely look. and listen. and tell your dad to give you a sign that he's still near.
it's been really hard for me adjusting to my mom's physical absence because we lived together and i miss her in this house, in my day-to-day existence where i could see her.
because of her physical death we were forced to enter into a new phase in our relationship--and i've come to understand that, in spite of her lack of physical presence, our relationship continues and so does our love for each other.
love doesn't die and apparently neither do we--not really. but losing someone from this physical dimension that we are currently in can be the hardest thing in the world. and because of that you have my deepest sympathy.