Occasional contact with retired PCs can be very useful as this makes the character available as a source of information, an adventure seed should they require help or die, or as a ready-made PC for a visiting player or a player who’s character dies, etc.
What are some palatable options for PC disappearance? Here are some ideas of mine and I’d love to hear suggestions.
“But (s)he’s so beautiful” Be they a tribal member in the jungle, an exotic local in East Asia, a bold and adventurous woman in an age when such is found generally disagreeable, or even the girl/boy next door, NPCs met in the course of adventure often have their allure. This is the “Felipe effect,”–Felipe being an associate of Lt. Colonel Percival Harrison Fawcett, who went off to get married during (after?) an expedition in Brazil.
Your comrade may drift into matrimonial bliss. Perhaps you’ll hear from the happy couple now and then: holiday cards, pictures of the kids. Perhaps there is an ominous silence.
“I just can’t handle it anymore” A PC may feel the need to “retire from active service” for some reason. In a game system with a madness mechanic they may be getting too close to the edge, or have gone over it. Of course, it may be necessary to check out old Professor McMasterson from the Home For Esteemed Wizards for that final showdown with the group’s arch-nemesis.
Perhaps the Investigator is having a crisis due to the deaths and injuries of bystanders, when the group demolished half of downtown during a huge fight with the villains.
Various other emotional and or personal situations may pull the PC away from adventuring, though this must be carefully handled by the player and GM so as to avoid a contrived feeling as the character exits into the wings. Maybe they just need more family time.
“I don’t feel so good” This is quite similar to “I just can’t handle it anymore,” but assumes a continued role for the PC to play off-screen. In a horror game, a departing PC can be an adventure seed for the GM when they begin to slowly dissolve, or bleed millions of spiders no entomologist can identify, then collapse like a deflated balloon, etc.
Lesser effects can leave a character available in a support role. Combat-induced dramatic injury, physical alteration etc. may make the PC a liability in the field, inappropriate looking/smelling in public or possess various other inconvenient qualities.
These folks may be able to do research, maintain relationships with important contacts and other useful tasks out of the limelight.
“I also am hyoo-mon” The PC can become infested with nanites or parasites, possessed by a demon or a mentally time-traveling alien being, hypno-controlled by a giant toad thing of god-like power squatting deep underground, replaced by a pod-person, be a duplicate secreted by some massive pool of ooze which absorbed the actual person, a doppleganger, a kill-bot etc.
This makes a ready-made villain to be destroyed in the next adventure, or perhaps an ongoing nemesis.
“Fell in the line of duty” Death of course is always an option, provided the player and GM avoid the aforementioned “arbitrarily hit by a truck.” I suggest the group not know of the plan to replace the character, as this removes all the drama when they throw themselves on the grenade, take a bullet for the President, dress up in a dynamite suit and run screaming down the mine shaft to ensure the cultists never get out alive, etc.