The final installment of Game of Thrones airs on AT&T's (NYSE:T) HBO over the weekend, and it should be another one for the record books. The penultimate episode last Sunday night attracted 12.5 million live viewers, and a season high 18.4 million folks when you factor in HBO Go and HBO Now streaming platforms. 

AT&T closed on its $85.4 billion deal for WarnerMedia last June, just as the seventh year of the fantasy drama television show came to a close. It has made the most of these final few episodes, but one is right to wonder what will become of HBO -- and now by proxy AT&T -- once the battle for the Iron Throne is settled on Sunday night. 

Blue smoke surrounding the AT&T logo.

Image source: AT&T.

One for the road

HBO won't be completely done with Game of Thrones after this weekend. It will be back next Sunday with The Last Watch, a two-hour documentary that details a behind-the-scenes look at the making of the show's final season. However, it will be shortly after that when HBO will be hit with a wave of cancellations. It's 2019. A lot of people will stop paying $15 a month for HBO Now or eliminate the channel from their premium cable packages once the channel's marquee show is done.

Fans of HBO will argue that there's a lot more to the network than just a single show that has anchored its programming for the last eight years. Veep is a critical fave. It's a perpetual Emmy grabber, but the Julia Louis-Dreyfus show just ran its series finale last week. Framing it for perspective, Veep's final entry reached a season-high just 1.1 million viewers -- or 1.6 million after factoring in HBO's streaming services. 

The baton at HBO will now be handed over to returning faves including Westworld, Big Little Lies, and Barry but there isn't any show on the platform drawing more than 1.6 million viewers a week. Game of Thrones will leave a void in the platform that already costs more than any of the other leading services. 

It will also be important to gauge the audience reaction to Sunday night's clincher. The same social media eruption that was in an uproar over petty things earlier this season like hard-to-see night battles or an errant Starbucks cup on the set has now turned on the show itself. Viewer ratings of the episodes on opinions aggregator Rotten Tomatoes have fallen sharply as the season plays out.

  • Season 8, Episode 1, "Winterfell": 92% approval rating
  • Season 8, Episode 2, "A Knight of the Seven Kingdoms": 88%
  • Season 8, Episode 3, "The Long Night": 75%
  • Season 8, Episode 4, "The Last of the Starks": 57%
  • Season 8, Episode 5, "The Bells": 47%

If the sixth and final episode isn't able to pull a rabbit -- or a dragon -- out of its hat, it will be a bad sign for the show's marketability in the future. The internet never forgives a bad ending, and it's hard to get folks to start a show that they already know has a notoriously rough ending. Sitcoms can survive a head-shaking finale. You can watch episodes of Seinfeld or How I Met Your Mother without fretting about the end, but it's a different story for serialized pieces when all the buildup is fumbled at the end. Good luck convincing someone to stream Dexter (35% approval for the final season after peaking at 98% a few seasons earlier) or Lost (which I'll shamefully admit that I'm in the minority who actually relished the way that one ended). 

AT&T sold off its minority stake in Hulu just as the final season of Game of Thrones was starting last month. It will have that much more riding on HBO as well the broader WarnerMedia premium streaming platform, which it expects to introduce in the fourth quarter of this year. It has one night to cement the legacy of Game of Thrones, and that's a battle that HBO can't afford to lose for the otherwise sluggish AT&T.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.