[Kuruharan]

Perhaps by the fact that they were running at break-neck speed towards the exit.

At the time they were running at break-neck speed for the exit he was hot on their tail (literally). He would have expected such behavior. When he set up his ambush they had been in the Twenty-first Hall and the Chamber of Mazarbul for several hours, which is where the dwarves had set up shop. He probably didn't want them gettin' ideas.

But the Ring was fast running out of options and on a one-way trip to doom

Actually, as the journey progressed its options were getting better and better with every step. You must take into account that Frodo himself failed in the end.

I suppose it still had the Boromir gambit up its (metaphorical) sleeve...but then its other options were pretty risky too.

(Lets see if we can't drag Boromir88 into the thread.)

Nah. As far as the Ring was concerned Boromir was a chump. He would have been putty in the Ring's (metaphorical) hands.

dwarves themselves were guilty of selfsame 'breaking and trespassing' in the first place, as they dug into Balrog's original habitat in the lower halls without any legal ground whatsoever.

Tut, tut councilor. That was not the Balrog's original habitat. The Balrog was trespassing without permission under other people's property (dwarven jurisprudence always draws property lines in a 360 degree circle in all directions around the center ).

Unless the Dwarves could tunnel into the Timeless Halls in search of mithril, they could not reach the Balrog's original habitat.