This sounds really normal, from what I've observed. When Linney passed away, we let Sundae have one last moment with her... she also nuzzled her face/eyes/ears and then eventually moved away. I believe it's them coming to terms with the fact that their friend has died. After we took Linney's body away and put Sundae back, Sundae would periodically wheek as if she wanted us to come and comfort her or keep her company. It was a behavior that she had never shown before, and it stopped again once we introduced a new guinea pig companion for her. She very obviously understood that Linney was gone and she was alone. They are definitely aware that they aren't coming back then... when one of our guinea pigs was ill and having multiple vet visits/surgeries, her companion was always really agitated whenever she was gone, waiting for her to come back. But after seeing the body when she finally passed, she was subdued and quiet, but no longer appeared to be worked up or actively looking for her friend afterwards.
