Yeah, that link about a third party intervening is 100% speculation based on zero evidence.
That said, it doesn't mean it's impossible. I mean, if Hisoka is to survive at this point, it's almost guaranteed that it will be the result of some deus ex machina factor -- a new ability from Hisoka we haven't seen before, some trap that Hisoka set during the fight that wasn't shown, a change of heart from Chrollo, or a third party who intervenes.
The good thing about HxH is that Togashi rarely employs deus ex machina sloppily. There are always major consequences, or at least well-conceived explanations. For example, Gon's miraculous defeat of Pitou required an entire arc to resolve. In any other shonen, that power-up would've cost him absolutely nothing.
If there is some third party who comes to the rescue, my guess is... Gon! Why?
Gon has a decent rapport with both Chrollo and Hisoka. He's also extremely charismatic and effective at causing people to have a change of heart. If anyone is in a position to convince Chrollo to spare Hisoka, it's Gon. Furthermore, he probably likes Hisoka, because Hisoka has helped him out several times in the past and taught him a lot about fighting, so he has every motivation to save him. On top of that, we know that Gon knows about Heaven's Arena, and is good enough by now to be a floor master himself. Finally, we haven't seen Gon in quite a while, and what more dramatic way would there be to bring him back into the picture?
My second guess would be someone from the Dark Continent arc. Perhaps one (or two) of the princes seeking body guards would want to recruit Chrollo and/or Hisoka? I could see both of these characters wanting to visit the Dark Continent, Hisoka for the challenge and Chrollo for the treasures.
That said, this is all pure speculation...