No nothing like that. If there was what is usually called "explosive" decompression, like a window blowing out, there will be a loud BANG, maybe a short howling sound as air rushes out, possibly fog will form in the cabin, and you will feel the air pressure in your head trying to get out until it equalizes. It might make your ear drums hurt until it does.
It depends on what you filed in your flight plan. To what point were you cleared? The key word in AIM 6-4-1,a.3. is “ When the clearance limit is a fix from which an approach begins”.
(c) Leave clearance limit.
(1) When the clearance limit is a fix from which an approach begins,
commence descent or descent and approach as close as possible to ...
You can descend from 4300' to 2600' as soon as you pass ZUNAD, as long as you remain in the protected airspace of the hold at ZUNAD.
It is the same situation if you were "Cleared for an approach" in a non-radar environment.
Sounds like a Forward Slip. It is not an unusual maneuver. It is very useful in order to descend faster than normal (Vertical Speed) without increasing your airspeed. The maneuver reduces the amount of lift generated while at the same time creating a large amount of drag by presenting the broad side of the fuselage to the relative wind.
Did the instructor ...
No, both would reach the ground at the same time, although the one with the higher airspeed would go farther before hitting the ground, assuming atmospheric conditions are invariant.
On the other hand, if both aircraft have the same flight path angle, the one with the higher airspeed would have a higher sink rate.