Actually, I don't see anywhere in the text in "Invading Clans" that the First Freemen were wiped out, only that they were no serious opposition.
The 4 main frontline units which made up the defenders of Rasalhague (First and Second Drakøn, First and Third Freemen) only had a combined strength of 2.3 regiments.
The 1st Drakøn was positioned on Rasalhague in 3049, while the Second Drakøn took heavy losses in fighting on New Caledonia (lost 2 battalions) and Verthandi before retreating to Rasalhague.
The Third Freemen likely had sent two battalions to Rasalhague from Kandis, with the third battalion being destroyed when Clan Wolf attacked Kandis in september 3050 (since the text in Clan Wolf SB says the remaining Third Freemen forces on Rasalhague surrendered, and yet faced a battalion on Kandis).
This leaves a battalion unaccounted for, so it must about a battalion of First Freemen forces which got off Last Frontier once they halted the Ghost Bear attack after putting their Khan in a coma.
Hope it clears things up.
With regards,
Øystein