It's a bit more extensive then that. The Thorns were confirmed by the head writer as still being on Galedon during the Jihad (Sarna is... spotty sometimes). This means that they died of one or more of the following:<br/><br/>Being killed by rampaging AFFS troops<br/>Caught in the initial outbreak of a bioweapon<br/>Being bombarded from orbit by the Snow Ravens<br/>Being taken prisoner by the Snow Ravens and caught on ships destroyed by their own fleet to contain the bioweapon outbreak<br/>Being still on-planet when the Combine nuked it form orbit to contain the biowepaon outbreak that the Ravens helped spread<br/><br/>So they're either very, very dead or radioactive mutant Zombies