(riot support response below)
Hey there, my name is Gunny and I'm here to assist you,
In the early days of League, we reserved summoner names for each new champion that came out. We did this mostly so that we could post on the site using those champions’ names, but also as a precaution against someone taking the name and pretending to be associated with Riot Games (we don’t let people put ‘Riot’ in their name for this reason). However, there is very little danger in players using champion names, and we no longer make posts under them, so we’ve stopped reserving champion names.
We won’t take champion names away from players who currently use them for any reason, although they are still subject to decay. If a player doesn’t log into an account for a certain period of time, their summoner name becomes free. We can’t share with you when an account will become inactive, but you can read more about it here:
Riot Games Player Support
May all your hits be crits and all your fails be tales!
Well this is very sad news... at least I have the answer now.