Whatever the story would be and whatever the tone would be, one thing is clear: to me VOY is VOY because it is about a ship lost in space. So in my movie they would somehow need to be sent back to the Delta Quadrant (definitely NOT a la Kirsten Beyer style) or even better, they should be sent outside the Milky Way galaxy into a different area of space.
Perhaps they could be sent on an undercover mission to avert a disaster to the Milky Way galaxy. The nature of the threat is such that people in the Milky Way mustn't find out about it - but Starfleet has already come up with a solution that could be carried out if a ship that already has expertise with survival in unknown regions accepts this mission. However, someone important in Starfleet knows that this is going to be a suicide mission from the start and does not share all the information relating to the mission.
When Voyager arrives, they will sooner or later realize that this is an impossible task so Janeway decides to go back at any costs. However, she will also realize that the mission is too important to be ignored since the whole Milky Way is in peril. So she decides to embark upon this long journey in the unknown areas ... but she is also planning to get back to Earth ... and so Voyager finds herself in the middle of where no one has gone before ...
The new galaxy is amazing: there is so much to discover. But can Janeway risk the mission just to please her explorer side? Of course not. So against her own nature she decides to ignore all the sights and stuff and focus on the mission. After all, the most important thing is to save her own galaxy right now.
But then something unexpected happens. There is some kind of natural barrier blocking her way where she needs to go to carry on with the mission. This is a distraction that needs to be dealt with asap. But how could she deal with it when she is just with one ship out there and apparently even the locals have never been able to dismantle it? That's tough. But the more she travels, the more she hears a rumour among the inhabitants of the new galaxy that there were once some aliens here who temporarily disabled the barrier. And as she hears more of this, descriptions of the alien race seem to be having an uncanny resemblance to Species 8472 ...
And yes, I know ... this is not one movie, this is the new Voyager show ...

Just an idea that has somehow sprung to mind.