I saw a video the other day of people having KBD, Bandos and more pets, that follow the player around. What do these do/are they tradeable?
http://services.runescape.com/m=news/boss-pets-and-spawn-rates?oldschool=1 I hope that answers your question, straight from the 07 homepage. They're non-tradeable to keep the rarity down.
They don't really "do" anything, they're more of a collectable, or a trophy, if you may. I guess it's a nice addition for PVMers, but I don't think they'll have THAT much of an impact in the game, unless they become tradeable.
I'm pretty sure you can't loose them once you get them; if you could it would be pretty ridiculous given that Jagex admitted it was an incredibly rare drop to get.
I'm pretty sure that their just like cats from the quest Gertude's Cat. They just follow you around and look cool lol.
In all seriousness, I wouldn't be too surprised if you were able to lose them. It is a rare drop, but you have to really try to lose a pet so my assumption is that if you were to somehow lose it, you won't be able to get it back somewhere, besides going back and trying to get it as a "Drop"
It's basically Gertrude's cat, I withdraw my Baby BD from the back, drop it and it follows me around.