In 5.2 your active pet team will take damage (10% of each of their health) when you forfeit. When previewed and tested on the PTR, this penalty also applied to not only wild battles but also Tamer battles. At the time, Mumper mentioned that it would likely stay that way for the time being.
However, he recently tweeted that the forfeit penalty will not apply to Tamer battles in an upcoming PTR build. Keep in mind that this is still all in the testing phase, so things could still change and nothing has been set in stone yet.
Still, this is good news. There's a chance that the penalty will only apply to wild battles, and the matches against Tamers will remain as they are now.
I'm personally hoping that the penalty not applying to Tamer battles, and I'm crossing my fingers that this decision will stick in 5.2. I have my reasons, but I'm sure developers have their own reasons for implementing it or not implementing it. Maybe there can be a compromise between the two sides. :)