GTA 6 launch doesn't necessarily mean definitive end for GTA Online. Take-Two's CEO explained what it depends on
Take-Two Interactive CEO Strauss Zelnick has hinted that GTA Online could be developed even when GTA 6 is released.

It might seem that with the release of GTA 6 (and, probably, a new version of the online game mode), Take-Two Interactive and its subsidiary Rockstar Games will decide to abandon the development of GTA Online. However, it turns out that the fate of the 10-year-old game isn't at all predetermined. At least that's the impression we could get from the words of Take-Two CEO, Strauss Zelnick.
During a recent conversation with IGN, he was asked why players should engage in GTA Online in 2025 when a new version of the game might appear with the launch of Grand Theft Auto VI. In his reply, Zelnick didn't refer to any unannounced online project from the GTA series, but he noted that Take-Two is recognized for backing games as long as the community remains interested.
As an example, the company's CEO mentioned NBA 2K Online, which hit the Chinese market in 2012 and wasn't phased out, even when a sequel to the online game launched there in 2017. Zelnick admitted that the company showed "a willingness to support legacy titles when a community wants to be engaged with them."
There's no need to worry about the latter in the case of GTA Online. Based on Steam's database charts, Rockstar's game is played by more than 150,000 people during peak times daily on Valve's platform. Thus, it's hard to expect that Take-Two would take such a drastic step as to move away from GTA Online, especially since GTA VI will initially only be available on consoles.