Considering that Albus Dumbledore (Jude Law) and Gellert Grindelwald (Mads Mikkelsen) meet face-to-face in destroy the blood pact and end Grindelwald's reign of terror.
Fantastic Beasts: The Crimes of Grindelwald ended with Newt Scamander (Eddie Redmayne) handing Dumbledore the blood pact, which he stole from Grindelwald via Niffler. When Newt asks the Hogwarts heaster, “Can we destroy it?” Dumbledore replies with a short "maybe." Perhaps he doesn't know what it will take, but it's just as (if not more) likely that he knows but is unsure if his plan will work out. Harry Potter fans know that by 1945, the blood pact will be destroyed, as that is when Dumbledore defeats Grindelwald in a historical duel. But judging by the second Fantastic Beasts 3 trailer, it seems like Dumbledore and Grindelwald will destroy the blood pact sooner, as the trailer shows them dueling each other freely.
The Fantastic Beasts 3 trailer shows Dumbledore and Grindelwald not only openly fighting each other but discussing inside what looks like a diner. This can mean that, in order to destroy the blood pact, both parties must agree to it. Dumbledore and Grindelwald's blood pact signifies a very intimate promise between the two (which is further explained by the fact that the two were romantically involved in the late 1890s). It's therefore highly unlikely that the pact can be destroyed by a simple spell, even if a powerful wizard like Dumbledore conjures it. Ending the blood pact can thus be seen as a kind of divorce, with Dumbledore and Grindelwald officially declaring war on each other.
During their conversation in the restaurant, Grindelwald tells Dumbledore, “With or without you, I’ll burn down their world.” He is referring, of course, to the Muggles' world, and even reminds Dumbledore he was the one who once said they could reshape the world. Indeed, Dumbledore is the one who first wrote to Grindelwald about seizing power over the Muggles "for the greater good" - a motto Grindelwald ended up using as an excuse for his atrocities against Muggles. In this Fantastic Beasts 3 scene, it seems like Grindelwald is giving Dumbledore one last chance to him in his war - perhaps Grindelwald is still hopeful Dumbledore will choose not to end the blood pact and forces with him, but even he must know that won't happen.
Grindelwald sitting down with Dumbledore promises to be a crucial scene for Fantastic Beasts: The Secrets of Dumbledore. For a while now, fans have waited for the five-movie series to further explore the wizards' complicated relationship. The blood pact is only one of many dimensions the scene could explore - but one way or another, the two will agree to end the blood pact as the Fantastic Beasts 3 trailer already showed Dumbledore and Grindelwald dueling each other.
