That all sounds correct. Plasma is more conductive than Earth's gaseous atmosphere by many orders of magnitude.
I think the arc usually forms a disconnect within 10 seconds or so, because of thermal turbulence it has helped induce in the surrounding air. Problem is, you don't want a line arcing for 10 seconds, because that can really do some damage.
Does 10 seconds sound about right? Or will it go on indefinitely? Of course, it's dependent on voltage, spacing, even geometry. I guess I mean in general.