Manus had not sent Muninn after them. He recognized the spell Voldemort had used this time. It came from Bone · Blood · Flesh.
The King Family Library also had a copy of that book. Although its Dark Magic was evil and bloody, surprisingly, it was not intended to harm people—the casting process might generally leave people rather worse for wear, but at least none of the spells were meant to cause harm.
Defense, healing, transferring damage, forcibly sustaining life, rebuilding a body... one could say the entire spellbook revolved around a single principle: staying alive by any means necessary.
Previously, Voldemort had only demonstrated his modified body. He had never used any of the book's spells against Dumbledore's attacks, so Manus had thought he might never have learned them.
But now that Voldemort had used one of them, he most likely knew the others too. He had simply trusted his modified body to withstand Dumbledore's attacks and had not bothered using them before.
In that case, without an Anti-Apparition Charm in place, unless Dumbledore revealed a trump card guaranteed to defeat Voldemort in one blow, he would never be able to kill him even if he caught up.
Voldemort had not fled alone, either. He had taken along a group of Death Eaters who had survived both the Fiendfyre and the Order of the Phoenix. They could serve as subordinates, but in the hands of a wizard who had learned the spells in Bone · Blood · Flesh, they could also serve as materials for healing injuries, transferring damage, and providing shields.
And if Dumbledore really had such a trump card, he would have used it just now.
"What a shame... after being caught in this trap, Voldemort will certainly be furious, but he'll also become more cautious."
Manus