Answer:
There's two possibilities, either nothing happens, or they are slowly eliminated from the population.
Step-by-step explanation:
Some adaptations are no longer useful, like wisdom teeth for us humans or hip bones in whales. Whales definitely don't need hip bones, but having them also doesn't really hurt their chances of survival. In these cases it doesn't matter, so the individuals remain in the population.
If the organism's chance of survival is decreased due to its adaptation no longer working, then it will be eliminated from the population through natural selection. For example, if an individual's camouflage stops working, they will be less likely to survive and reproduce.