Will Ben and Lisa Braedon ever come back to the series (just watched S6 E21 in Germany) and can'z find the information.

no they end up leaving because dean had castiel erase ben and lisa's memories of him because he didnt want them to get hurt anymore

the episode is 21 of season 6 named Let It Bleed

So far it looks like they won't come back. But this is supernatural where nothing is impossible and even death can't keep characters away.

It's doubtful. A lot of the fan disliked Lisa, and oleh the end the writes were just listening to the fan in menulis her out. They couldn't keep Ben without his mom.

But they're both still alive, so I guess there's still a slim potential chance.

Ok