It's complicated. First, France sometimes conducts trials in abstentia, but probably would not in this one. Normally, a trial without the defendant physically present is only held if the victim is French and the accused has evaded prosecution by leaving France.

The normal procedure in a case like this one would be to issue an international arrest warrant for the accused. Extradition would be unlikely, but the accused would have to mind their p's and q's rather carefully when traveling internationally.

They would not be able to transit France or French possessions, nor would they be able to travel to a set number of nations which have liberal criminal-cooperation agreements with France.

So, you know, no French Caribbean vacations, no French Polynesia, etc. — and even travel to a handful of countries in Europe would be highly problematic considering the arrest warrants.

All in all, however, it's unlikely we'll ever see a trial. The U.K. and the U.S. have very different legal systems to France, and are highly reluctant to extradite to France unless the offense in question also violates U.K. or U.S. law, respectively.