Sorry, I will be really honest with you;
I hate when something dies, even plants. So I kinda prefer to avoid "death threads".
This whole section is kinda a "try to avoid" thing for me. I know it hurts a lot when something you cared died, try hugging a pillow, that's my e-hug for you.
But things will work out, try thinking that he's in a better place now, and you cared for him and he's thankful for all the attention you gave him throughout the years.
Just smile and say "Buddy, we had a long run, and we enjoyed every moment of it, thanks a lot for your company, the moments we both were down, the moments we played, all of it. I hope you can hear me saying this and I wish you luck in what's ahead of you, if you ever wish to come back to me in a new run, let me know and I will make sure to save 5 bucks to buy you straight away from the market again! May you rest in peace buddy!"