The 'good' news is that I'm sure you'll be on the flight: economy is relatively quiet. That's bad news for upgrades, however... of course it could still be that you will be upgraded, or someone else will.

If, somehow, you are downgraded, you will be entitled to 3/4 of the one-way ticket price back in compensation. Downgrades and involuntary denied boarding are rare, but interesting enough to get reported on. Do make sure you check in online as soon as you can and get to the airport early though, just in case.