Pay the ticket, save the miles.
50k miles vs $500? That's an easy choice, pay for the ticket. Right now i just was looking at flights vs miles on MVD-ATL. It's a $2000 ticket in mid January, but 60,000 miles. That's 3 cents per mile, vs 1 cent which you'd get on the europe trip.
The only reason to take the miles option is if you have a LOT of miles and aren't using them.