A lot (didn't say all) of "holster without looking" theory is predicated on cowboy-western-movie notions of "expert gun handling". It has more to do with looking like you "know what you are doing" than doing what is necessary or prudent.
The rougher Force-on-Force and CQB training I've done strongly suggests to me that my clothes and the holster may not be where I expect them to be, (or where they have been in less physical training) in any situation where I actually have to defend my life with a gun.
Add to this the known physical effects of threat-to-life circumstances, and it starts to sound like a recipe for something ugly. I've read enough stories of the good guy getting shot by police (because he was holding a gun) to make me believe it's a good idea to put that sucker away as soon as it is safe to do so.
I've read enough stories of ND-on-reholstering, under comparatively calm, day-at-the-range circumstances to make me believe that it's more important to be safe than to look good.
The smartest advice seems to be that you shouldn't be holstering unless it is thought safe enough to do so. "Safe enough" means that the known threat is down and you've done what it necessary to insure that there are no other known threats. Having gained some combination of distance and cover, a quick glance upon reholstering, and keeping a hand on the weapon until authorities arrive ... seems like no downside to that approach.