Wizards are not naturally immortal, in fact creating their own form of immortality is their graduate thesis.
“I have created a perpetual healing spell.”
“A classic. Congratulations.”
“If my soul leaves my body, this spell will keep it around and lucid enough to magic myself back together.”
“Effective. Next?”
“My spell feeds off the life force of microscopic things! When bacteria die near me, it adds to my total. Wiping down the sink with antibacterial cleaner gives me SUCH a buzz; I think I may have to dial it down a bit.”
“…I would be very curious to see your notes about this spell.”