If you believe in such things, presumably the universe will restore the balance somehow. Maybe evil gets a bunch of lucky breaks. Maybe a lot of paragons of good get corrupted.
Funny thing: for a long time I've thought restoring balance to the Force was exactly what Darth Vader did by wiping out all those Jedi who were unbalancing it towards the Light Side.
although we do still have a time machine, so I wouldn't completely rule out the possibility.