ok, that's interesting. So what you are proposing is that Algrim dies and goes to Hel, and then Thor and co are in Hel, and maybe Hela decides to change him to Kurse then and there and fight Thor? And then in the course of that Kurse realizes how Malekith (and maybe Hela too) betrayed him, and he helps Thor and co get away by fighting as Skurge does at the bridge? That would take away that revenge moment with Malekith maybe, unless he somehow survives that and is able to leave Hel somehow.
Okay so, giving this a bit more consideration, in the comics at one point we have Thor sending Kurse (who now hates Malekith) down to Hel to torment Hela, another story I read about Thor inhabits the Destroyers body and wreaks havoc in Hel to make Hela break a spell she has on him. SO. What we could get, is Algrim dying and going to Hel, Thor, Loki, and possibly jane and others travelling to Hel to free those mortal souls and/or find and free Frigga, and/or retrieve some item(s) stolen from Odin's vault in the attack on the palace. Then instead of a wrestling match with Hela (the one where she scars him and he wears a mask) to win their freedom, we get the warriors having to defeat all of those who they have defeated in battle, and that's where Algrim appears again. Hela is impressed by his hatred of Thor and decides to give him a boost (and maybe earlier they've stolen something that can do that from Odin's vault, such as the Tesseract in the previous attack, if Hela can't do something like that herself). So we get Kurse vs Thor in Hel. During the course of this, things are looking hopeless, Thor is tied up with Kurse and the dead warriors of the past are so many that his companions are having a tough time. (this is possibly the big Iceland battle, Niffleheim instead of Svartalfheim, I know Chris E. was there too, but he may not have been involved with that particular part of filming, or maybe he is down there in Hel with Hela plotting when the gang arrives, and escapes, I don't know...)
Just when all seems lost, Kurse is given a tremendous blast of lightning, or something like that, to stun him, and he finally remembers that Malekith betrayed him, and his attention and hate turns to focus on that. (if Malekith is there, maybe he is taunting Kurse for still failing to kill Thor, and that's when Kurse remembers, then Malekith makes a quick exit before Kurse can have his revenge). To Hela's horror Kurse starts tearing apart Hel itself, she begs Thor to stop him, help her. This is where giving her a McGuffin from Odin's vault to change Kurse (rather than her doing herself) is helpful because she then may not have a way to change him back or stop him, especially if that item is broken or lost in the course of the fighting. Anyway, Thor agrees to stop him but only in exchange for her letting those souls go, and Frigga go, and whatever else he wants. She agrees and they stun Kurse again, knocking him out so she can imprison him somewhere, and she keeps her word and lets those souls go, but... she didn't agree to let them all go peacefully so we still get more of those dead warriors going after them on the way out.
Later, if we have Malekith and Kurse surviving Thor 2 (with Kurse imprisoned in Hel, but potentially could break out or be let out later), then we could get the culmination of that in Thor 3 or maybe it'll fit in Thor 2. I'm just saying, it was spread out and divided up in the comics, so it may be so in the film, and that makes Malekith available to come back working with Surtur in Thor 3.
By the way, AM, it occurs to me, if they use this, "you must face all the warriors you've killed in battle" thing, then having warriors that are the ordinary people of Asgard, people who have NOT killed before, go into this fight in Hel, would actually make more sense strategically. Because by having those experienced warriors go in, or warriors of Valhalla, mathematically, the experienced warrriors are going to mean those fighting against them are going to be that many more, whereas if we are just talking about those who Thor, Loki, and Sif/Warriors 3 have killed in battle, with the help of these new warriors who have never killed, then the odds seem better... strangely enough.
