Natural selection isn't some benevolent deity. Its MO is to drive species to extinction, it's just that when some individuals find a way around it we call that evolution.
Without knowing which traits a species "needs", the best conservationists can do is to increase numbers while preserving diversity. The "50% of all females laying rim eggs" is just a reflection of the single breeding pair's genomes. If rim eggs had been discarded, only copies of the "good" genes could have been tossed along with those eggs, and "bad" genes inadvertently selected by virtue of not being linked to the rim egg gene - which was exactly how the rim egg gene itself came to be in the last breeding pair.
Increasing numbers while preserving diversity will give the bottlenecked gene pool a chance to mix into as many combinations as possible before being released back into the wild, without natural selection driving the species to extinction. It doesn't always work, but if it doesn't work the species was done for regardless of our efforts.
Without knowing which traits a species "needs", the best conservationists can do is to increase numbers while preserving diversity. The "50% of all females laying rim eggs" is just a reflection of the single breeding pair's genomes. If rim eggs had been discarded, only copies of the "good" genes could have been tossed along with those eggs, and "bad" genes inadvertently selected by virtue of not being linked to the rim egg gene - which was exactly how the rim egg gene itself came to be in the last breeding pair.
Increasing numbers while preserving diversity will give the bottlenecked gene pool a chance to mix into as many combinations as possible before being released back into the wild, without natural selection driving the species to extinction. It doesn't always work, but if it doesn't work the species was done for regardless of our efforts.