>>12768578>>12783698Before battle:
"Hey, <player>! What brings you here? Your Pokémon don't look dead! I can at least make them faint! Let's go, pal!"
After player wins:
"What? You stinker!" I took it easy on you too!"
After battle:
"How's your Pokédex coming, pal? I just caught a Cubone! I can't find the grown-up Marowak yet! I doubt there are any left! Well I better get going! I've got a lot to accomplish, pal! Smell ya later!"
I know it's a popular theory and all, but there is nothing much to validate it besides him not battling with a Raticate and being battled at the Pokémon Tower. He sounds like his same cocky self, not like someone who went to mourn a fallen friend. In fact, he even says he was looking for a Marowak and settled for a Cubone.
Besides, who's to say he didn't evolve his Raticate and then box it? Blue says he caught a Cubone and yet we never battle against it. In fact, despite having several more unmentioned Pokémon (Quote from S.S. Anne battle: "Bonjour! <player>! Imagine seeing you here! <player>, were you really invited? So how's your Pokédex coming? I already caught 40 kinds, pal! Different kinds are everywhere! Crawl around in grassy areas!") he only actually battles with a full team of six on Route 22 and as Champion.
Yes, yes, it's a popular fan theory and all and makes the game grittier and darker, yadda yadda, but I really don't see much validation for it.