Sorry about your pet! To answer your question, they will always give you back what you used to trade. So, if you traded your own UC for that specific...
Thanks @Great White North for the Wolfy Ryu and @Hollow for the Kousetsu puppy <)
Thanks @sugarbee for my howling wolfy and @hearts for my wolfy pumpkin <3
Thanks @Lyrichord for my custom userbars and @Houndoom for my star puppy :3