400 Jockey - given that some of CX management have worked for all of those airlines you have mentioned and some of those airlines management have worked for, at least, two of the others on your list then I would have to say, YES, don't for one minute imagine that, if there is any doubt, they will use their contacts from previous companies to 'check', they do, it happens all the time and eventually the bad eggs are discovered.
C152 Capt. If all that happened was an unrecorded 'phone call between two colleagues then it would be hard to establish grounds for a law suite.
Inciter - are you ex CX, failed CX or what? Anyway up you are not being very realistic.
Airlines with commercial numbers like CX and SIA are way up there on the list of 'airlines we need to emulate' for many carriers, including some North American and some European.
Yeager - as you can see from PPRuNe, airline pilots will gossip like a bunch of chicken and when times get hard they will eat their own young. If you leave any airline, big or small, under suspicious circumstances, you can rest assured your past will eventually catch you up, if you have in any way mislead your new employer about your past you are a candidate for immediate dismissal, it is usually written in the very first paragraphs of a contract.