At what point does "leave no man behind" come at too high a price?

The US military takes pride in the "leave no man behind" concept.  Its a promise to each servicemember that all efforts will be made to save you if possible.

At what point does it become too high a price?  Before you answer reflexively that its a point of honor and everything must be done, consider this passage from an Army War College Case Study of the Bat 21 incident by Lt Col Stanley Busboom, United States Air Force (this is a cached page, its easily accessed online though).

When SAMs struck the Bat 21 EB-66, five men were lost; that is a sunk cost that precedes all others in this story.2 On the same day, a UH-1H making a rescue attempt was gunned down with the loss of four lives.  Two OV-10s went down to SAMs with two creymimbers lost, a third becoming a POW, the fourth escaping.4 Six more lives (five cremen and a combat photographer) were lost when the Jolly Green rescue chopper went down on the rescue attempt. There is no single authoritative source that accounts for all of these men together, or suggests other losses in Sandys or strike
aircraft that flew on supporting missions. If the foregoing compilation is accepted, at least 17 combat deaths are relevant to the Bat 21 story.  From one perspective, the loss of these aviators may be the least problematic of the analysis. All were flying combat missions and were well  aware of the risks involved in the line of duty. On the other hand, it is possible to argue that the UH-1H crew was not on a properly planned mission
and was unduly put in harm's way. Similarly, the Jolly Green crew was sent in through withering fire--but then there was also a communication error in that sequence of events.

Thats the losses from the air side of the house.  Check this out from Wikipedia... 

Maj. David A. Brookbank, a U.S. Air Force liaison with the 3rd Division, reported, "The operation cost the 3rd ARVN dearly." He concluded that the restriction gave the North Vietnamese "an opportunity unprecedented in the annals of warfare to advance at will." He stated, "It seems logical to assume that many South Vietnamese troops died because air and artillery support were not available."[3]:120 He warned his superiors that the 3rd Division's officers resented the fact that the 7th Air Force would put thousands of South Vietnamese soldiers' lives at risk to rescue one of their own.[18]:318
American response to the NVA operation virtually ground to a halt[16]:251 as air resources were diverted to support the recovery, and for a few days defense of the northern border area was second in priority to rescuing Hambleton.[18]:318

One man went down and at least 17 other fliers died to recover him.  It doesn't count the heavy losses that the ARVN suffered because they were denied air, sea and artillery fire support.

Was it worth it?

Did the "leave no man behind" concept come at too high a price?

This question has particular importance to the USMC.  Tactical Recovery of Aircraft and Personnel is a hallmark mission of the Marine Expeditionary Unit.  The O'Grady Rescue and the recovery of the downed F-15 pilots in Libya were successful.  But we were lucky.  Mechanical problems, a stray bullet or a lucky RPG shot could knock down a helo and suddenly you have a squad of Marines along with the pilots they sought to rescue becoming bait for a meeting engagement no one saw coming.  In the future, at what point does it become a case of cutting losses and accepting the capture and/or public beheading of US personnel?  Or do we accept any losses to get back one or two pilots that went down in bad guy land?  I just don't know.