Game of Thrones showrunner seems pretty confident that a spinoff series is going to happen

It certainly is the smart bet.

Are you worried about not having any more Game of Thrones? You're probably wasting your energy on those thoughts. Questions about the future of the series are popping up as the current showrunners begin preparations for the launch of Season 7 and the answers seem to keep pointing towards a continuation. Shocking, I know. In a panel at SXSW, David Benioff revealed that he felt like HBO was looking to keep Game of Thrones going in some capacity.

He said:

"The characters who maybe will survive — there’s always going to be this temptation to keep doing it… to do the spinoff show or do the sequel show and everything. And I think HBO might well do one."

He continued:

"I’m looking forward to watching it, I think it’ll be great, but I think it’s better for them to get new blood in with new visions."

So basically if/when this spinoff show does happen, Benioff and Weiss more than likely will not be a part of it. It was previously revealed that HBO was having 'preliminary ongoing talks' with Game of Thrones creator, George R.R. Martin. But where exactly those conversations have led, remains unknown.  

Obviously, this all still remains to be seen, but with Game of Thrones being far and away the biggest attraction for the network's HBO GO subscription package, a drop off in that revenue is not something they are looking forward to. Unless the network can come up with an equally titanic show in the next two years, it seems logical that Season 8 is not the end of Game of Thrones for all time.

Source: [Buzzfeed via GamesRadar