I raised my objections at the time to that scene. Not only is A'lars a 2nd generation Earth born Eternal with near skyfather power levels, baseline Earth Eternal physical attributes should have prevented Thanos from simply "punching" through him like that. Not saying he has Class 100 strength and durability, but probably more in line with Zuras or somewhat lower. His baseline is going to be higher than most Earth Eternals since he was there when the initial cosmic incident happened.
Between his physiology and advanced Titanian medical technology, etc, I expect he'll make a full recovery eventually. But even Eternals can take a while to recover from injuries severe enough--back in the 90s Starfox was rendered comatose for weeks after being injured in a battle with a cosmically-powered Nebula.
Words cannot express how disappointed I am that Cates teased us with Darkhawk being a member, only to pull a bait and switch and have him sucked into a cosmic vortex in the first issue. Is there any hope that he'll actually be a part of the team?
Was wondering if the Eternals were resurrected by the end of Final Host.
Apparently in Gaiman's Eternal V3, Eternals can be repaired.
So I doubt if Eros's disfigure will be permanent.