I guess this is the right place for Sanshiki stuff, even if it's not particularly spoilery. He put up bits of an interview with Shu and producer Takebe
from Hyper Hobby.
She said that Ankh was always destined to end like he did--they considered sealing him in the end, but it didn't work out. They never even discussed keeping him alive. However, turning Eiji into a Greeed was added along the way.
Eiji's grandfather is the Japanese Prime Minister so he uses his mother's name to avoid being recognized. His older brother is also an elite politician. (Shu didn't know Eiji had an older brother. :sweat
Shu wanted to do action with explosions and stuff and didn't get to in the show, so producer Takebe said she'd talk to the Movie War writer (probably she purposely didn't give the name).
Knowing this, personally I'd say they probably won't bring him back since it would wreck the ending.