At any pivot point can you get absolute '0' deflection?
No. Pivoting left or right from your bridge at the pivot point is an aiming adjustment which counteracts the deflection of your shaft. For instance, if you pivot the tip to the right, you are aiming more to the right (v. if you parallel shift the whole cue to the right), and because the cue ball will deflect to the left, aiming more to the right will counteract the deflection. The pivot point is where the aiming adjustment is exactly equal to the net deflection (squirt - swerve). I'm not quite up to speed on the particulars of the pivot point, but the harder you hit the cue ball, the less swerve there is, which results in more net deflection, which means the pivot point must change based on the speed of your shot.**
And if you do, what happens when you increase your pivot point?
If you mean, what happens when you increase your bridge length, the answer is: the aiming adjustment is less for the same tip position on the cue ball, i.e. the angle into the cue ball is smaller, which means the aiming adjustment is not enough to compensate for all of the net deflection. As your bridge length gets shorter, in order to pivot your cue to the desired tip position, you have to move the butt of the cue more.
And by the way, the pivot point concept does not take into account how the spin on the cue ball will throw the object ball, so even if you have the pivot point correct for a given shot, you still have to adjust your aim for how the spin on the cue ball will throw the object ball.
** Dr. Dave actually defines the pivot point relative to one particular shot: a short, fast shot where swerve is 0. Are all your shots short and fast? Probably not, so don't think that once you've found the pivot point for a short, fast shot, that the same bridge length is going to offset the deflection for other shots. Think...break shot. While not short, a break shot is fast. Find the pivot point for your break speed and if possible use that bridge length on break shots.