It wouldn't be impossible to overcome outside the demo, so take heart. Rebels might occupy things, but you can end your wars and deal with them bit by bit. The game, like life, has no compunction against hitting you while your down. You will be attacked and ravaged because you're weak and helpless. England wasted 100 years trying to conquer France to no avail, so the game will let you do the same. I think perhaps the best thing you can keep in mind for EU4 is to never let yourself become that weak, even for an instant. Take your time and keep reserves of everything.

Oh yeah...well anyway wait for TuesdayNo saving in the demo, unfortunately.