WARNING: The following contains spoilers for Star Wars: War of the Bounty Hunters #1 by Charles Soule, Luke Ross, Neeraj Menon and VC's Travis Lanham, on sale now.
The Mandalorian helped to solidify the legend of Boba Fett, giving viewers a chance to see the ruthlessness of one of the most dangerous bounty hunters in the galaxy. Outside of comics and novels, that had not been seen until The Mandalorian, where Fett slaughtered countless stormtroopers as he helped Din Djarin to recover Grogu. However, one of Fett's kills felt more significant than the others. Star Wars: War of the Bounty Hunters #1 showed just how personal Fett's disposal of Bib Fortuna was.
In accordance with the Empire, Fett acquired Han Solo's body entrapped in carbonite and was en route to Jabba the Hutt's Palace. Unfortunately for Fett, the carbonite was failing. Though he was able to find a doctor to restore the carbonite, Solo was stolen while Fett was away from the clinic. After discovering Solo's kidnapping, Fett returned to his ship and was confronted by the bounty hunters Zuckuss and 4-LOM. He quickly disposed of them and took 4-LOM's droid head to his ship where Boba learned that Jabba the Hutt had placed a bounty on his own head. This led him to return to Tatooine for answers.
Fett arrived at Jabba's Palace in an extremely confrontational mood. He was greeted at the gates by Bib Fortuna and a pair of Gamorrean guards. Boba killed both the guards to show the seriousness of his visit. Fortuna informed Fett that Jabba had placed a bounty on his head because he took too long to bring Solo and received word that another party had come into possession of the carbonite slab. Fett demanded to speak with Jabba but was informed that Jabba was discussing an invitation received from Crimson Dawn with the other Hutts.
As Fortuna had given all of the information Fett requested, he assumed that the bounty hunter would be on his way. The underbelly of Tatooine appeared at the gates from the inside of Jabba's Palace. Boba threatened everyone present and promised to kill anyone who stood in his way. He demanded to see the invitation and Fortuna obliged. After Boba viewed the invitation, he made a further demand that Fortuna would repair his ship.
It's clear from these interactions that Boba took the bounty on his head personally. He could not hash it out with Jabba the Hutt, so he settled for threatening Jabba's second in command. Fortuna was Jabba's most trusted confidant. Not only did he grant visitors access to the palace, but he also represented Jabba off-world. War of the Bounty Hunters expands upon Fortuna's role by Jabba's side as he took control of the palace when the Hutt was off-world.
These events would serve as the strongest purpose for Fett's revenge on Fortuna in The Mandalorian. While Fortuna would have been present at Boba Fett's assumed death in the Sarlacc Pit, he did not play a vital role. He could have searched for Fett, but he definitely had other priorities at the time. Fett knew how close Jabba and Fortuna were. It is extremely likely that he would have blamed Fortuna just as much as Jabba for the bounty placed on his head.
Boba has suspended grudges on countless occasions if it serves a grander purpose. While he might have suspended his grudge on Jabba and Fortuna during the events of Return of the Jedi, Jabba's death would have diminished that purpose. Boba would not have forgotten how Fortuna and Jabba treated him when his bounty was stolen. Boba's visit to Jabba's Palace in War of the Bounty Hunters could prove to be the beginning tension that led to Bib Fortuna's death in The Mandalorian.