I had Titan-egi die a few times... Like, three. That was imediatly followed by me using swiftcast->Summon. I summoned Titan-egi if the monster I was attacking is dead, or Garuda/Ifrit if it wasn't to help me finish it.
So, literally no problem whatsoever with the removal of Sustain.

You guys have to understand that it's not because Titan-egi isn't immortal anymore that you can't use it. It's a HP buffer which act as a tempoary shield before the enemy starts attacking you. And it's completly fine that way.
Besides, swapping Egi is a thing now. Better start now.