You should ask your probation officer for permission to go. If you violate the terms of your probation...your likely to go to the pokey. You agreed to the plea deal, the deal was good enough then and now you wanna change the deal. There is always a possibility that the probation will show up and you run a risk of being detained in customs.
Personally, I wouldn't have bought the ticket, this could very well end up being the most expensive price you've ever paid to go to Europe!
I'd also like to add that you run a greater chance of getting caught upon your return to the US. Getting out isn't nearly as much of a problem as getting back in these days (this is from my personal experience).

