There has been much talk about "what you would do" in certain situations. No one really knows until they are faced with the problem - theory and practice as so different.
Airlines would hopefully seek out the informant to the authorities and get their details. It makes excellent
pr anyway for an airline to contact the informant and make them feel as though they have done the right thing - on balance of course they are trying to find out exactly how/why they reported this matter. Do it under the guise of "we are hoping to make our detection rates of these matters better by learning" - say that an informant will probably feel they are high almighty and special and gush out information like there is no tomorrow.
If any vindictiveness is found in the informant's intentions then a clear letter from the airline would be in order that they intend to seek damages and make an example - BUT you would have to prove a link between the two of them to make it clear there was malicious play afoot....