Extending my "poetic justice" snark from above, I would have found it a somewhat depressing but also very noble ending to the series if, after seeing that the revised timeline was generally worse for people, Our Heroes made the decision to undo their own shortcut because they realized that in their efforts to 'save themselves' they'd screwed everyone else.
Even if that resulted in a, "And they were never seen again..." ending (for the time-being), we'd know that Our Heroes were still out there doing good.
Even if that resulted in a, "And they were never seen again..." ending (for the time-being), we'd know that Our Heroes were still out there doing good.