The miners you free from the quarry tower run outside and disappear, so either they can climb better that you can as a dragon knight, or (more likely) they have a spell or device to protect them from the poison (air quality being a major concern in mines). At least some of the people not mentioned in Aleroth may have escaped the poison (don't know how thorough Damian's troops were, though), and headed somewhere other than the fjords or Aleroth.
On Sentinel Island, Michael was building a raft...
[spoiler]and made it away from the island, at least. You can find the raft (and his diary) hung up on a rock north east of the island.
