The only character with any durability who was killed was Colossus, although killing him is very impressive. Loki shows some pretty good durability, I think close to him or at least about like Angel Dust (who Colossus fought pretty closely). His knives would prob cut right through earth metals. Would he be able to carve up a big Colossus metal Sentinel? Not sure. If the Sentinel could go all "Colossus" and still form pokey arms and still use fire-face, Loki would get beat majority. I think he can tank fire for short periods and cut even the armored form, if not easily. He fought with Thor for awhile. I think he could go toe to toe with Angel Dust physically, and maybe Colossus. And his knives plus illusions would give him a lot of help. He gets a few wins with knives. Yay.
Also: I think Angel Dust getting ragdolled by Hulk would prob knock her out, and would stun colossus about like Loki was. So I think Loki is comparable in durability to Colossus.