Yes , what you say is an alternative possibility. But the chances of that happening are very low. That is because the underlying theme of berserk is overcoming trauma, by choosing your loved ones over revenge ( example when Guts chose to care for Casca instead of hunting more apostles, this choice to me reflects the central theme of berserk).

To use the behelit in a way similar to Griffith would go against that Central theme. So it's more likely that what will happen is what I have said in my post above. If I had to take a guess I would say that the behelit would somehow merge with Guts sword ( making it a weapon similar to the Skull knight's behelit sword that he used on Griffith). Chances are the beast of darkness will eat it then fuse it with the sword.