[Faceman]

where exactly is your last save?
Sola should be standing where the Spore colonies were before. You can talk him into letting him do the quest yourself and then talk the snirv into giving you the helmet.
You CAN fight your way out of the underdark (through the Western Tunnels which are BTW not marked on the map but ARE there) but you'll miss out on some interesting quests.
If you have a save at the very beginning of the quest, make sure you read all the dialogue and pay special attention to time limits. Then follow everything and it should be alright.