Maybe the question was meant to be if English is going to remain as a "procedural language", that is one of those few languages used for the internal business of the Commission. Currently they are English, German, French. More about that at https://en.wikipedia.org/wiki/Languages_of_the_European_Unio...

My bet is yes, even if Ireland and Malta were leaving the EU: everybody knows English, only a few know any other language.