The original Overwatch will be incorporated into the upcoming game.
The original Overwatch's days seem to be numbered as a standalone product as it will integrate with Overwatch 2.
Speaking in a recent AMA on Reddit, game director Aaron Keller confirmed what Blizzard stated previously when it said the Overwatch and Overwatch 2 clients will merge to avoid fragmenting the player base.
"When Overwatch 2 launches on October 4, it will be a replacement for the current Live Service," said Keller.
Blizzard pretty much confirmed this when it first announced Overwatch 2 at BlizzCon 2019 stating it was part of the team's mantra of no player left behind, as former game director Jeff Kaplan said during the event.
The AMA also reiterated that all cosmetics and loot boxes will transfer over to Overwatch 2 upon release. Since the game will not contain loot boxes, unopened boxes will magically open upon transfer.
This too reiterates a previous comment made by Blizzard at BlizzCon 2019 when it stated all Overwatch cosmetics and progress will carry forward into Overwatch 2.
When the game releases, you can expect the free-to-play live experience to feature regular seasonal updates and a Battle Pass featuring new content such as heroes, game modes, maps, cosmetics, and more. Season One of the game will feature the new heroes Sojourn, Junker Queen, and an unannounced support hero alongside the new 5v5 PvP experience. You can also expect reworked heroes, new maps and modes, and a reimagined competitive experience.
Blizzard also recently provided a roadmap to give beta participants, Early Access, and prospective Overwatch 2 players an idea of what to expect with December's Season 2 and beyond.
Overwatch 2 will be released for PC, PS4, PS5, Switch, Xbox One, and Xbox Series X/S. It will feature cross-progression and cross-play as well.