If you're aware of it, then you have no reason to not stop it. Like I said, extending a Sim's life on purpose is against the rules so technically it's not allowed. However, that being said, there is a difference between a pet doing it and you being unable to cancel it and you just letting the pet do it. I think there is a certain time frame you have to cancel the action but I haven't tried it as it's so random I haven't had another pet try to keep anyone alive in a while.
I'm also fairly certain that a pet will only do it at the end of someone's life so you can't bank on that happening if it's an accident. And I don't know about anyone else but I don't remember a time when I didn't want someone to die in my dynasty file as space is such a high commodity.