If a character insists on breaking off from the group, e.g. to run back to town buy a fishing net and a bottle of wine, instead of roleplaying what happens, secretly roll a d%.
01 Character dies. Other characters will have to search for the body if they want to find it.
02 Character is lying unconscious but stable at -5 hp in an alley or wilderness as appropriate.
03 Character is being held in the local constabulary or by some other neutral party for some infraction until a 50gp fine is paid by the characters.
04 Character is lying drunk and passed out in a brothel (even if he or she is a character that would never do such a thing.)
05 Character is in the middle of a tense high-stakes card game. Character has lost 100gp or all money if less.
06 Character has been enchanted (charmed, entranced, hypnotized, suggested, dominated or geased) and is currently doing some embarassing chore for his or her enchanter.
07 Character has become lost and is currently 2d20 miles from where he or she should be. Roll a d8 to determine direction.
08 Character has gone domestic and is in the middle of a marriage ceremony when/if characters arrive.
09 Character has found religion or is suddenly feeling repentent if already religious and is kneeling and praying in a temple when encountered by characters.
10 Character has inspired the rage of the town or some other appropriate neutral group who is chasing the character when encountered by the other characters.
11-99 Character completes the task he or she set out to do and returns in an appropriate amount of time.
00 Character somehow manages to complete the task in record time, what might have taken 3 hours, instead only takes 3 minutes. Perhaps a merchant just happened to be passing by or some other appropriate act of providence.
Note: On a roll of 01 to 10, the character will never return and instead the players will have to search for him/her. If they choose not to, then the player will simply have to roll up another character, never knowing what happened to the last character. The DM need not come up with any explanation or rational for what happened to the character when discovered, however the character may make any explanation he or she likes and the other characters may or may not choose to believe it if they like.