My Favorite Fix for Absent Player(s)

It happens. The group has scheduled a session and at the last minute something comes up that prevents a player (or players) from attending. 

First, determine if the group should even meet. Things to consider:

• Frequency of the group's gathering
• Cancelling a game that only meets once a month hurts a lot more than a group that meets every Tues and Thurs for a couple of hours.
• Percentage of participants who will miss the session
• A group of 7 missing 1 player is less impacted than a group of 4 missing 2 players.
• Location of the party at the end of the last session
• If your sessions tend to end with the party arriving back at their base of operations it is a lot easier to address any absenteeism as opposed to if your session ended in the middle of a melee encounter.
  

If the group decides to still meet and continue where the last game left off, there are some "generic" options that are often employed.

• The referee (or one of the other players) controls the character of the absent player(s) if the last session ended mid-adventure.
• The issue I've seen with this solution is the fallout if the absent player's character is killed. I know it's all supposed to be fun gaming, but players can get attached to their characters, and character death is bad enough without it happening while someone else is "at the wheel."
  
 

• The character(s) of the absent player(s) stays behind if the last session ended with the group safely back at their "base of operations." 
• This might get complicated if the group embarks on another dungeon delve or similar adventure that takes more than one session to resolve; getting the absent characters reunited with the party may present a challenge to the adventure's continuity.
  

Here's a solution that I've used (with minor variations) in my medieval fantasy themed games.

The "Summon Monster" spells in AD&D summons monsters for the spellcaster. The exact verbage of the spell is below, with my emphasis bold and italicized:

Explanation/Description: Within 1-4 rounds of casting this spell, the magic-

user will cause the appearance of from 2-8 first level monsters (selected at random by the referee, but whose number may be either randomly determined or selected personally by the referee, according to the strength of the monster randomly determined). These monsters will appear in the spot, within spell range, desired by the magic-user, and they will attack the spell user’s opponents to the best of their ability until he or she commands that attack cease, or the spell duration expires, or the monsters are slain. <snip>

 
My fix is to attribute a player character's sudden disappearance mid-game to a high level caster somewhere else in the game world having cast "Summon Monster" of adequate level to include the absent player('s) character(s) which results in them being instantly "summoned away" by the spell (usually with some visual effect akin to the transporter in Star Trek.)

This puts the absent character(s) in a sort of "limbo" which allows the players assembled to continue without having to track the absent player(s)' character(s), and frees the referee to focus on the game at hand. The absent character(s) can reappear whenever the absent player(s) rejoins the game under the explanation that the "summon monster" spell has been dispelled, returning the formerly absent player(s) character(s) into the company of their previous companions when the spell was originally cast.

I used to have a small table to determine how the "summoned" characters fared in their time away from the party, and it's probably only fair to have some sort of repercussion for missing a scheduled session, but as one who understands how complicated real life can be I'd suggest a lenient table of consequences.

A variation of the above solution was used for a slightly different scenario, but it offered here as another fix.

I had one player in one group who always wanted to play, but their attendance rate was absolutely atrocious due to an insane work schedule. Since this player was a good friend to all in the group, we decided to accept the explanation that the character was cursed to randomly phase into the ethereal plane, rendering them unable to communicate in any way, shape or form with the party. The ethereal character could tag along, but was unable to contribute anything, harm or be harmed, earn experience points, and as such was "not present but attending." When the player could attend a session, the character phased back to the Prime Material Plane, and when the player missed the next session, well... you get the picture.

Feel free to drop you own creative solutions to address absentee players.