Final battle can go on for a loooooooooooooooooooong time. Naruto has been in its final battle for like 5 years. Bleach is in it's final battle too (apparently), and it's never ending. This could be Beel's final arc, but it'll be made up of a bunch of events and shit, so no real worries here.
The difference is that Naruto makes a loooot of money and Bleach still makes a lot of money. Beelzebub makes not nearly as much money as those two plus it is in bottom (of money making and rank) of the magazine.
WSJ has a very certain way of ending/cancelling series. New series are given a 3 week notice that they are ending. Semi popular series who went for over 100 chapters get a certain amount of chapters from them to end it. The exact number is not known well but Shaman King got 20 chapters. So when a series suddenly accelerates its pace like Beelzebub did it is a clear sign of ending/being cancelled.
The cancellation/ending round has already started. 4 new series are going to enter the magazine which means 3-4 old series are going to get cancelled. Beelzebub seems to be one of them.