airlines love having the discretion of firing you once you start being disagreeable. i'm sure they would not hesitate to exercise that provision if they know you are just feigning sickness out of a number of reasons (having other priorities, some sort of protest, act of defiance, plain laziness).
having said that, at the end of the day, the airline is still a business. i'm sure you can make your own estimate on how much it costs to screen and hire a new pilot. so it makes better sense for them to keep you (provided you've been quite professional in your work) rather than source out a new guy EVEN IF YOU HAVE BEEN SICK FOR MORE THAN THE STIPULATED 5 CONSECUTIVE DAYS.
there are lots of examples of guys in VNA getting sick or having motorbike accidents who had to be away for a couple of months in some cases, and still got to keep their jobs. in fact, there wasn't even any salary deductions made on them. their time away was just treated as vacation brought forward, i.e., offsetted in their future vacation days. these things i know for a fact, not just in VNA but in a lot of other airlines.
rest easy and enjoy Vietnam