Mentor Job Hazards

Forget logging or fishing or coal-mining-- in Fantasyland, Wise Old Mentors have the highest death rate among pretty much any profession except the Dark Lord's bodyguards.
Now, the mentor is a key figure from the Hero's Journey plot archtype, and it also makes sense on a metaphorical level for the character to die. After all, the hero needs to continue on alone without the mentor to bail them out of trouble. Symbolically, it's also the transfer of responsibility to the next generation, the future supplanting the past.
That said, this archetype has turned into a cliche plot device, where the mentor exists to tell the main character how special they are, give them instant training in their special skill, and then die to provide angst and a possible revenge plot. Instead of any significant symbolism, they're a walking info dump in an Alec Guinness skinsuit.
If you are using the Hero's Journey as a template, that's one thing. But if your mentor is nothing more than a walking, talking Wikipedia page on the main character's backstory or special abilities or quest goals, you might consider another means to get that information across. Better still, revising the methods for delivering info can mean major changes to the plot, and get rid of some of the more annoying cliches in fantasy. For example, why not have the character's parents train them to use their gift? What about having a gift that's not unique, and having to sit though 'using fire magic without causing horrible destruction' classes in school, the way lots of us had to sit though Home Ec/Health? Even a long-term relationship with the mentor-- maybe is a relative who shares their talent, or a respected community member who regularly takes on students-- is much more interesting than having someone who swoops in to do a round of improbably fast teaching and then kick the bucket.