Ranger pets seem like a touchy subject at a lot of tables I've been to. Players seem to feel like the pets are an extension of their character. DMs see them as NPCs they can use to get to the ranger. Definitely worth a session zero discussion.
— Nate (@renegadenate) October 10, 2019
Your companion creature in D&D—whether a familiar, a beast companion, or something else—is both a monster/NPC and an extension of your character. Whatever can happen to a creature—beneficial or harmful—can happen to your companion, unless a rule says otherwise. #DnD https://t.co/uatGyWhDia
— Jeremy Crawford (@JeremyECrawford) October 10, 2019
I feel like that doesn’t answer the issue whatsoever. It wasn’t a rules lawyering thing, it was that DMs and players have different perspectives on what to do with companions.
I agree, it’s not really about rules lawyering. I think the question kind of answers itself: it requires a session zero talk between dm & player about how vulnerable a companion would be. if a player intends to build around that companion as a tank or other heavily-used combat or utility mechanic, that needs to be clear to the dm, because in that case it is a character extension. removing a pet would remove how that character fundamentally interacts with the world.
however, if a pet is only used occasionally (as a joke or bonus perception roll, for example) and the player seems to forget about their care or companionship except at very (in)opportune times, they need to be honest with themselves about what purpose a pet serves: a plot-convenient npc. in which case, if they are sent into a situation unprepared, they are subject to the same threats as any other creature npc. a dm may feel the need to remind the PC that they don’t actually treat their pet that well, and that has consequences for a character ostensibly designed around their companion.
a neglected pet has every reason to escape; depending on the PC, loyalty from one’s pet is not a given. how a player treats their pet can change through the game, especially if a ranger “learns” how to use them effectively. the story might require that pet & master spend time apart, and reconvene having learned something new about what they need from each other. regardless of how it plays out, the answer is this: ranger pets ARE both character choice and NPC, and can be treated as either one according to the actions and interactions of the PC. it’s the players’ responsibility to use their pets well, and the dm’s responsibility to help a player realize their pet’s potential and play fairly with what the player wants to achieve.