If you include the Left Behind DLC, The Last of Us Part 1 is roughly 16 hours long. The controversial follow-up, The Last of Us Part II, is bigger and longer at 30 hours. Thus, the discussion following the show's renewal is if The Last of Us on HBO will take multiple seasons to adapt the sequel.
Now, the show's creators, Craig Mazin and Neil Druckmann, have confirmed that the adaptation of The Last of Us Part II will take place across "multiple seasons".
In an interview with GQ U.K., Mazin and Druckmann entertained questions about the show. One question, in particular, was about the show's "sacred" ending.
Mazin revealed that the director, Ali Abbasi, had toyed around with the idea of making the sequence last longer, featuring "[Joel and Ellie] walking, not really together but apart, down towards Jackson." Mazin and the rest of the team ultimately went with the same ending as the game, with a "close-up of Ellie."
Later on, when the interviewer asked the co-creators about The Last us Season 2, Druckmann had a very direct answer "it's more than one season."
Mazin later clarified the statement, saying "you have noted correctly that we will not say how many. But more than one is factually correct."
TLDR; be prepared for multiple seasons of The Last of Us.
HBO's The Last of Us showed that the story of the original source material still has plenty of room for improvement when told through another medium. The changes made to the Cordyceps infection and the additional details about Ellie's mum are all unique to the show.
As it is based on a much longer and more nuanced game, The Last of Us on HBO could technically go on for more than three seasons based exclusively on the source material.
If we were to speculate, Season 2 and Season 3 could tell the stories of Ellie and Abbie, respectively, changing perspectives, similar to The Last of Us Part II.
We also can't deny that Neil Druckmann and Craig Mazin could come up with completely original stories set following the events of both games. Forbes' Paul Tassi has an interesting theory about Season 4 of The Last of Us coming after The Last of Us Part III comes out on the PS6 sometime later this decade.
It's an interesting take based on limited information, but you can't deny that it's a plausible scenario.
At the end of the day, we should be glad we got to witness what's easily the best video game adaptation of all time. It's now up to God of War, Twisted Metal, Horizon, and Fallout, among others, to try and live up to the expectations.