I role play the "monster" and decide what he would do.
Many times, they just disappear.
Sometimes, they do evil plots.
Sometimes, they are not particularly evil (Meepo, and a goblin merchant) and go do their thing (Meepo: try to take over the kobold tribe -- he succeeded based on my random determination method of whether the new blood or the old dynasty won the Democratic nomination!; goblin merchant -- sell stuff and occassionally appear as flavor).
Many times, they just disappear.
Sometimes, they do evil plots.
Sometimes, they are not particularly evil (Meepo, and a goblin merchant) and go do their thing (Meepo: try to take over the kobold tribe -- he succeeded based on my random determination method of whether the new blood or the old dynasty won the Democratic nomination!; goblin merchant -- sell stuff and occassionally appear as flavor).