Llednar Twem is not so much an alter ego, as an aspect of Mewts personality - so long as Mewt exists, so does Llednar. Llednar being destroyed was showing that Mewt - the source of his existence was gone. However, this should not be taken as being his "death". Llednar is only in relative terms alive.
Also, the plot looks cool. BUT, and I BEG of you here, dont give in to pressure and bring back Mewt. HE IS GONE!