I have always had two cats – bonded pairs. I have always been lucky that when one cat passes away, the remaining cat has accepted a new cat into the household, and become close enough to them to bond very closely. It has taken from a day to 8 months for the bonding to take place, but they are always really close in the end.
I have done this because I have always worked and never want my cat to be lonely at home. These pairs of cats do everything together, including playing, and this keeps them stimulated.
The bad part is that when one of the pair dies, the remaining cat is very sad, and lost. We usually euthanise at home, and show the remaining cat the body of their departed friend. They are able to sniff and spend time with their late buddy, and it seems to help them accept the loss better. We also diffuse Feliway Classic in times of stress.
Sadly, when Fluffy passed recently, Ziggy hid away. Fluffy had ‘mothered’ him since he was a tiny kitten and I think he knew something was very wrong. Mollie and Harley could ‘say their goodbyes’ and have adapted well, but Ziggy didn’t. He has spent since then deeply depressed and miserable. He refuses to even enter the room where Fluffy died. It is so hard because you cannot talk to them to explain anything. I hope time helps.