We've had plenty of discussions about when and who may use Guts' behelit, and while I won't say that I believe this is exactly what will go down, (nor do I wish it) I will say there's precedent in the story for this little theory.
Let's start by taking a look at the the original Black Swordsman arc. It was said by the Godhand when speaking with the Count (an apostle that has already made a sacrifice) that the purpose of the sacrifice is to "sever any last remnants of your own humanity". Ultimately we know that the Count DOES NOT make a sacrifice and is thus pulled in to hell by what appears to be the people he's killed.
Now imagine if we do manage to see this scenario return. For a moment, imagine that Guts has managed to defeat Griffith, and the behelit summons the Godhand, but not for Guts, but for Griffith again. We know that if Griffith is to wish to remain alive he would need to "sever any last remnants of his own humanity". What humanity has Griffith still have left? His dream. He chose to sacrifice the first time to attain it, yet it's the only thing of meaning to him left for him to sacrifice. This is how Falconia and it's people will be sacrificed, as a few people may have speculated.
However I'm having a hard time believing this would happen. If Griffith did sacrifice Falconia then the same logic that lead him to sacrifice during the Eclipse would be the same reasoning to stop him for going any further. "You're the only one who ever made me forget my dream", do you think that Griffith would sacrifice the city and it's people? I don't think he would. Instead I would think it much more likely that Griffith would realize that sacrificing the city and his dream now, would mean everything was for nothing. All those bones, all those people he stepped on to get the kingdom, and for what? To sacrifice them in the end to continue to be Godhand?
What might be much more likely, is that Griffith does not choose to sacrifice at all. Instead he's pulled into the vortex by those he's killed, those he's sacrificed. Imagine for a moment the original Band of Hawk members pulling him into the vortex as he chooses to not make the sacrifice. "The thread of fate has been severed", and all those at the ceremony that were to be sacrificed would be present and would witness it. All of Falconia would realize who it was they were relying on and what he almost did to continue to live. Would this be redemption? Probably not. Would this be the way I would like to see Griffith go out? Again, probably not. But I can't help thinking that perhaps there's a reason we've gone all these years without Miura giving us the fight we want to see happen.
Perhaps in the end Griffith will choose to not forget his dream again. Thoughts? Theories? I've not come across any other threads that have brought up the possibility that Griffith may use the behelit again in the future.
I was going to type out some more, but it's 4am.