After announcing the release date for Overwatch 2: Invasion over the weekend, Blizzard has no confirmed you'll have to pay for the new PvE content.
At this point it seems that Blizzard can't decide what it wants to do with Overwatch. It seems kind of baffling how they've handled what is basically a live service cash cow.
The only reason I would go back and play overwatch 1 every once in a while was for the free pve events. I'd then get sucked into pvp again for a bit, spend some money without thinking, and then leave again. If they start charging for pve events I won't be tempted back into that loop.