I'm pretty sure they are meant to be killable, but it's also meant to be very hard and require co-ordinated efforts by multiple ships. Could be wrong here.
Ticket it, sounds like a bug. Personally I hope they don't just explode into space dust Michael Bay style. I want them to list and roll out of control disabled and burning, something that big just doesn't go "poof" into nothing.
Yeah, It's not like I just showed up and had a little go at it, I grinded this thing for 90 mins, I too was expecting it to jump away, or at least something. Ticketed it anyways.