WARNING: This contains spoilers for Obi-Wan Kenobi.
Obi-Wan Kenobi episode 5 saw two Inquisitors survive what appeared to be lethal lightsaber injuries, but there is an in-universe reason for this not-so-uncommon Star Wars trope. Despite the fact the fate of the Grand Inquisitor had already been settled by Star Wars Rebels, Obi-Wan Kenobi bet on a cliffhanger regarding the character's apparent death at the end of episode 2. From then on, the Third Sister Reva, one of the few characters in Obi-Wan Kenobi whose fate is a mystery, took the lead both in terms of the Inquisitor's internal disputes and the show's main storyline.SCREENRANT VIDEO OF THE DAY
As Reva finally came close to capturing Obi-Wan, it was revealed that the Third Sister's plans were much bigger than becoming Grand Inquisitor. In fact, the only reason Reva wanted to succeed in the Inquisitors' most difficult hunt yet was so she could get close enough to kill Darth Vader, the person responsible for the death of many younglings at the Jedi Temple. However, Vader was already fully aware that Reva was a surviving Jedi youngling, and everything that had happened after the Grand Inquisitor's apparent death had been an act by Vader.
Related: Obi-Wan's Anakin Flashbacks Are More Important Than You Realize
That said, the Grand Inquisitor's injury by a lightsaber at the end of Obi-Wan Kenobi episode 2 was very real, and so was Reva's at the end of her fight against Darth Vader in episode 5. Still, both characters survived being stabbed by lightsabers, with the Grand Inquisitor seemingly already fully recovered by the time he returns to gloat over a wounded Reva. More than a decade ago in canon, something similar happened to Darth Maul, who had been cut in half by Obi-Wan but survived and returned in Star Wars: The Clone Wars to almost become the leader of Mandalore. The explanation as to why those dark side users escaped certain death in a way that Jedi like Qui-Gon Jinn never could is summarized by the Grand Inquisitor's quote in Obi-Wan Kenobi episode 5: "Revenge does wonders for the will to live, don't you think?". It's precisely the hate and the wish for revenge that kept the Grand Inquisitor, Reva, and Darth Maul alive on each of these occasions. Unlike the Jedi and other light-side-aligned warriors, those who use the dark side of the Force see no problem with harvesting anger and hate for power, and as such, the two Inquisitors and the former Sith Lord managed to keep themselves alive against all odds using this hatred.
The idea that sheer hate and revenge alone could maintain a person alive originates from "Brothers," an episode from Clone Wars season 4. Maul himself wasn't so sure about what had happened to him at the time, but he was confident that his hatred for Obi-Wan Kenobi, and perhaps even for his former master Darth Sidious, had kept him alive after falling into the melting pit in Star Wars: Episode I - The Phantom Menace. While that could have remained as a one-time-only retcon, Star Wars is now embracing that piece of lore with the Grand Inquisitor and the Third Sister.
Yoda said to Luke in Dagobah that the dark side of the Force is "quicker" and "easier," and that is somewhat proved by how Inquisitors and Sith have managed to survive what should have been fatal lightsaber injuries in canon. More than a decade after Darth Maul's return, the unnatural ways of the dark side have once again proven incredibly potent in Obi-Wan Kenobi. That said, Star Wars must be careful not to use this dark side ability as a cheap plot device to create cliffhangers and retcon deaths - or the franchise risks undermining the highly impactful stories of Darth Maul, the Grand Inquisitor, and Reva.