I'm not sure why we are assuming that in-decline tokens removed from a region by the use of a Lava token are discarded? The rule sheet that comes with the expansion specifically says: "there is no loss of tokens". This doesn't seem at all unclear.
Ok, I think tokens of in-decline race (other than Ghouls) should be removed as there is no way player can redeploy them.
Ghouls are special case and may or may not be an exception (?) because they can be treated and redeployed like tokens of active race.