You can recruit troops from the elven garrison near the city in the upper left corner – and that's 15 dragons, etc. Is that how it's supposed to be? Near the central bridge, you can also get about 150 archers, etc. Basically, I took these archers with Wingom and defeated all the enemies on auto-battle, and returned Glenheim. I'll take the dragons; then I can start clearing out the garrisons for Winlend.
When recapturing Glenheim, the console also complains that the function CaptureHavenTown2 is unknown. I checked, and there is indeed no such function in the script.