In Star Trek TNG Episode 11 "The Big Goodbye", why would the people inside of the holodeck "vanish" if the program aborts?

Whilst the TV series of TNG is pretty inconsistent on what physical effects are possible, the film "Star Trek: First Contact" makes it explicit that the holodeck certainly can "interact" with matter.

Picard uses a holodeck gun to kill two Borg, and it works. In order to do it he has to disable some safety cutouts, but it's clearly possible and the holodeck bullets do normal damage.

In the pilot episode of TNG, "Encounter at Farpoint", Data indicated that the environments created within holodecks are a mixture of holographic simulations and real matter.

RIKER: I didn't believe these simulations could be this real.

DATA: Much of it is real, sir. If the transporters can convert our bodies to an energy beam, then back to the original pattern...

RIKER: Yes, of course. And these rocks and vegetations have much simpler patterns.

DATA: Correct, sir.

This was further expanded upon within the Star Trek: The Next Generation Technical Manual.

The Holodeck utilizes two main subsystems, the holographic imagery subsystem and the matter conversion subsystem. The holographic imagery subsection creates the realistic background environments. The matter conversion subsystem creates physical "props" from the starship's central raw matter supplies. Under normal conditions, a participant in a Holodeck simulation should not be able to detect differences between a real object and a simulated one.

The Holodeck also generates remarkably lifelike recreations of humanoids or other lifeforms. Such animated characters are composed of solid matter arranged by transporter-based replicators and manipulated by highly advanced computer-driven tractor beams. The results are exceptionally realistic "puppets", which exhibit behaviours almost exactly like those of living beings, depending on software limits. Transporter-based matter replication is, of course, incapable of duplicating an actual living being.

Objects created on the Holodeck that are pure holographic images cannot be removed from the Holodeck, even if they appear to possess physical reality because of the focused forcebeam imagery. Objects created by replicator matter conversion do have physical reality and can indeed be removed from the Holodeck, even though they will no longer be under computer control.

When a holodeck program is ended, any real matter created by that program, and still present within the holodeck, is presumably converted back into energy by the matter conversion subsystem. (The same apparently does not apply to matter which is no longer in the holodeck when the program is ended, as was the case when Picard left a holodeck with a lipstick mark on his face in "The Big Goodbye".)

This isn't presented as something that could endanger real people when a holodeck is functioning normally, as we've seen programs ended with people still inside holodecks on multiple occasions. However, if a holodeck is malfunctioning -- as was the case during "The Big Goodbye" -- perhaps there's a risk that real people within a holodeck could be dematerialised if a program is summarily aborted from the outside. This is apparently what Wesley was concerned about.