Last week, within 2 days of each other, we lost our beloved 11 year old dogs. We are both having to cope with ghost dogs and the cats who miss them.
I don't know what your day to day interactions with Kirby were, but I am completely sure you are still starting to do them and then suddenly realizing that he's not there.
I haven't decided which of us is the more "fortunate". I was with Maddie in our living room when she died and you weren't able to be with Kirby. But, on the other hand, you get to remember Kirby as Kirby and not have to deal with the intermediate steps of Kirby to animatronic Kirby to not Kirby. My memories of Maddie will always be overlaid with her actual ending. My husband and kids, while they have the intellectual knowledge of what happened at the end, in their hearts have the happy happy dog who is no more.
The big difference between our losses is that you are the artist of a popular strip with thousands of followers and I'm not. The people who know about my Maddie are people who also knew her and grieve for me and with me out of personal knowledge. You have to deal with the few people who genuinely understand your grief to those who sympathize with you but don't quite know how to express it to those who are taking the opportunistic to moment to say "Hey Scott!! Look at me. I'll come up with something that will show you how deep and cool I am".
I am one of the first group, especially in the timing. You have my complete empathy and sorrow and I wish I could tell you how soon you will not have this terrible emptiness, but I can't because I still have that same emptiness myself...