Apparently, Cannes' declaration of "persona non grata" does not put a filmmaker out of reach for the Palme D'Or.
While it would be easy to presume that the festival's statement that Lars Von Trier was now an "unwelcome person" also extended to his film, it does not.
However, it does mean that Von Trier would not be a welcome presence at the ceremony. Per global news agency AFP:
Questioned by AFP, the festival said that von Trier's exclusion means he could in theory still win the Palme d'Or for which his film is in competition but he would not be allowed to attend the ceremony to accept it.
Someone who attended the meeting said the decree meant that von Trier "remains in competition but is asked to be discreet. So, if he wins a prize on Sunday, he's asked not to come and receive it."
So at this point, out of the five films that are considered frontrunners for the top prize (per indieWIRE critic Eric Kohn), there's a 40% chance that the director would choose not to be there to accept it.