You should run ALL your characters through the first couple of levels until ALL of them have a fighting chance. It's laborous, I know, but pretty soon you will have a mage/priest combo (example) that could take other Mage/priests through and protect them while their XP goes up. Also, a powerful mage in a low level dungeon with only 1 or 2 others can get XP that does not have to be split 6 ways.
I played Wiz 1-5 on an Apple IIe and had to save each time the party returned to the Inn... Save to DISC!!!! So I know your frustration. But a fairly powerful fighter/mage combo can rack up lottsa XP in a short time by 'whupping' those 'small humanoid fleas' over and over. The mage gets off a spell faster (allowing fewer 'small humanoids to flee') and the fighter mops up the rest. Also, if a PC changes professions and drops back down to L1, he/she can take short romps with higher level PC's and rack up XP, and levels, at an impressive rate.
As for having PC's left in the dungeon, send a second party of 4 PC's and bring them out two at a time.
FYI. Some areas of the dungeon are 'damped' against Magic.
Son of FYI. LOKTOFEIT, if memory serves, requires you to know exactly where you are in the Dungeon (X-Y coordinates) and exactly where you are going. If not accurate, the spell will fizzle or... transport you into solid rock. No rescue party needed there.
Grandson of FYI. Save, save, save.
who wouldn't dream of leaving the Inn without a Lord on one arm and a Bishop on the other.
"All that we can name
is but a Game within a Game".
m.t.bear, torn from the
clammy grasp of e.a.poe