That could work, but it would feel like a massive missed opportunity as the idea, at least as far as Johns take on the character, was that Abin Sur's death was what finally broke Sinestro and pushed him to the dark side. Having Sinestro be the one who killed Abin would certainly be a cool take, but it would rush things a bit too much for my liking.
I guess I'm used to adaptations always changing the source material and if they don't hand over Sinestro's relationship with Hal to another Earth GL, then I sort of see Abin as the best compromise. Could also work if they gave it a tragic spin with Sinestro unwillingly killing him after failing to persuade him that the Guardians' methods were ineffective and that's what pushes him to the dark side. Something that Abin could also indirectly warn Hal about while he gives him the ring. Too much fan fiction I guess but isn't that what most adaptations do anyway.
For when my rants on the forums just aren’t enough: https://thevindicativevordan.tumblr.com/