One of my old cats was a resue cat with his mum and had both been treated very cruelly in the past. Sadly the mum died, she got blood poisening from very bad teeth, they were very unfriendly cats due to their treatment but they did love eachother. When she died, her sone went on to actually come and sit with you, not let you pick him up, nor close both doors to a room, but gradually he got a little bit more loving, missing his mum.
I truly believe animals miss friends and relatives, they miss and remember owners so why not their animal buddies.
I agree with the last reply about a new buddy!