when i was about 15-16 years old, my dog [1/2 poodle] had some kind of back issue that left him paralyzed from the waist down. the vet basically said there wasn't anything that could be done to repair him [this was about 35 years ago, btw]. he wasn't in any pain, & could drag himself around by his front paws... but he'd also lost bladder/bowel control, so he was pretty much banned from the house. he also was rubbing the tops of his rear paws raw from the dragging.
my parents finally convinced me to allow him to be PTS. at that time, i said something about seeing him in Heaven, & my mom questioned me. this is what i said [& i still believe it] - "once i'm in Heaven, if i want him, he'll be there."
i don't pretend to know exactly what we'll see in Heaven - but i do believe that we'll be happy. if our pets are not there, it'll be because we'll be happy w/o them. here on earth, we simply cannot conceive that could be true - but Paul said it best:
1 Corinthians 13:12 (The Message)
12We don't yet see things clearly. We're squinting in a fog, peering through a mist. But it won't be long before the weather clears and the sun shines bright! We'll see it all then, see it all as clearly as God sees us, knowing him directly just as he knows us!
so, if we want them, they'll be there. i just don't know for certain that i will want them once i get there.