In the end of Secrets of Dumbledore, when
Grindewald and Dumbledore duel, we can clearly see that Grindelwald has the Elder Wand in his hand.
We know that Dumbledore is one of the best wizards to live, but this should not even compare to
Grindewald plus Elder Wand.
Also, I believe that
The Blood Pact cannot "protect" someone, just cause damage to the person who tries to harm the another. The duel between the two is evidence of that.
How is it possible that Dumbledore is alive?
While it is a powerful wand, the Elder Wand is not an unbeatable wand. In fact, when Dumbledore famously defeated Grindelwald in 1945 (yet to happen in the timeline of Fantastic Beasts), Grindelwald had the Elder Wand and was its master, since mastery of it passed to Dumbledore.
“And Grindelwald used the Elder Wand to become powerful. And at the height of his power, when Dumbledore knew he was the only one who could stop him, he duelled Grindelwald, and beat him, and he took the Elder Wand.”
- Harry Potter and the Deathly Hallows, Chapter 24 (The Wandmaker)
In the notes for “The Tale of the Three Brothers” in “The Tales of Beedle the Bard”, Dumbledore himself explained that while the Elder Wand is a powerful wand, the idea that it is a wand that is impossible to beat is not supported by the facts of its passage through the hands of many owners.
“What must strike any intelligent witch or wizard on studying the so-called history of the Elder Wand is that every man who claims to have owned it28 has insisted that it is “unbeatable,” when the known facts of its passage through many owners’ hands demonstrate that has it not only been beaten hundreds of times, but that it also attracts trouble as Grumble the Grubby Goat attracted flies.”
- The Tales of Beedle the Bard
In addition to Dumbledore’s defeat of Grindelwald, at least one other historical case of a wizard beating the owner of the Elder Wand in a duel is known - Loxias, who beat Barnabas Deverill. Loxias was described as being ‘equally notorious’ in reputation as Barnabas Deverill, so this seems to imply they were somewhat similarly skilled.
“All that is certain is that a wand called the “Eldrun27 Wand” by its owner, Barnabas Deverill, appeared in the early eighteenth century, and that Deverill used it to carve himself out a reputation as a fearsome warlock, until his reign of terror was ended by the equally notorious Loxias, who took the wand, rechristened it the “Deathstick,” and used it to lay waste to anyone who displeased him.”
- The Tales of Beedle the Bard
Therefore, Grindelwald owning the Elder Wand does not make it impossible for him to be beaten in a duel.
