I did missions, but 'X' and Solberg don't give me spells. Only one of the two gives you spells for any one act. Solberg gives you spells for wiping out the Slimes or Roaches, and X gives you spells for taking out the troglodytes and golems. Also, if you've already obtained the spells they give you, they give you nothing. As time passes, towns crumble.
People become refugees.
However, it never becomes impossible to finish the game. You never stop being able to buy food, or identification. The important NPCs never die. However, I suggest having a pretty strong party by around Day 170 or so. At the time of this writing, no nasty bugs have been found in Exile III for Windows.