In the Jedi Academy Trilogy, Dark Force Rising, and even Darksaber you see a lot of stuff closer to what is being done in the trailers of this game. In Champions of the Force the Jedi students, not even full fledged Jedi, were able to push back an entire Imperial attack force that included more than 1 Star Destroyer, with a little concentration.
As for the in game story, dead characters need to be dead end of discussion. But for the vs. mode sure bring back anyone you want. Just also make sure that characters who haven't been born yet or are still little kids are showing up as full grown adults either for the story mode.