If Hela and most of Hel exists in the micro verse...then her role really is "small"
The lower realms enter into the negative side of things. Muspelheim is more like a physical hell and where Hela is currently trapped, in the lowest levels of reality, is sort of like a Hell that exists so far beneath the surface. Only souls/life energy goes there. Niffleheim still exists, but Hel's power is banished to the inside of reality, so that Hela can't escape. Surtur has basically been stopped once before and Hela's link to death and resurrection is what's bringing him back along with Malekith. The Vanir know something is up, that Ragnarok is approaching but are deceived into being on the wrong side of the war at first. They think someone else will start Ragnarok.
She's a mostly hidden force on the inside of existence, along with Surtur. Hiding in the shadows, until the line that divides the shadow side from physical existence is blurred, and merges the two sides together again...
They only exist in the twilight spaces between dimensions and times right now. Odin tried to trap them from all time and existence, but they're gathering energy through Malekith's partial connection to the dark side.
What if she's controlling the Old crone at one point of the story, and Jane, as well as finally Darcy? We wouldn't see much of Hela. And she's trying to bring Surtur back to life along with Malekith, except she's working from the bottom of the world tree, while Malekith starts from the top. Both are trying to initiate Ragnarok for Surtur because they've been promised to have their reign's expanded. She stays in the shadowy side of existence along with Surtur working from/gnawing at the roots of the world tree. Working through Midgard.
What if parts of Hel and Muspellheim no longer exist in the physical side of reality due to Odin's temporal vortex trapping Surtur and Hela in the negative, or dark side of existence. Malekith has partial access to all the dark sides of existence through the dark world, and the division along his face ties into this. He exists partially in a twilight between the dark side, and the physical side of existence. Malekith's looking to merge many realities and bring them back to physical existence through Stone Henge.
This helps make the future hard to predict, and like with the Mandarin every decision/point of impact counts. AIM already understands some of this by the end of IM3...
Malekith intends to unlock these forces that are trapped in the microverse/dark-matter/immaterial/anti-matter/negative side of reality.
If Hela is trapped in between dimensions and helping Surtur/Malekith complete twilight by collecting souls, then we may not see the actress playing her that much... This would be the only reason such powerful beings like Hela and Surtur have to work through Midguard and Jane Foster/ Seek out Malekith's help again... They've been trapped by a temporal vortex... A punishment briefly considered for Loki. This has all happened before in the past... Ragnarok always returns.
For the record, I think Fox is about to screw up time-travel. Marvel knows they have to do this slowly and make any time/timeline viewing/time travel different from what's going on in DoFP...
This is what Feige's recent talk about taking risks is about.
If some of these risks play out we'll see Pym trapping some of the masters of Evil in the negative Zone/prison 42 & some elements of civil war in Avengers 2.