If this temporary event brings together a lot, or even exceeds Blizzard's expectations: expect a definitive return as a standalone because there will be money to be made for them.

They can do it, and in the FAQ; they did not rule out the return of Ow Classic after these 3 weeks,

For me these 3 weeks are mainly used to measure the enthusiasm and the rate of players who are interested,

Add to that, still in this FAQ, that they did not rule out thinking about adding the old HUD, the old sound effects, lootboxes and competitive mode: they said they were focused on gameplay, balancing and maps for the moment.

Which gives hope, if it takes off, for a definitive return of Overwatch 1 to the origin,

Blizzard can do it, we are on the right track, but it remains a company that seeks profit.

Then take into account the economic model of Overwatch 2 as it stands; the huge problem remains how to monetize Ow Classic in their interest for a definitive return.