Like with all sudden systems failures it was a front for a coup
To alleviate any panic, Letters still appears to be in charge but he is in fact a puppet, a Quisling if you will for the true rulers.
This is a temporary measure to secure and consolidate power, after which time Letters will be liquidated
The business trip was a front so that he would be out of the country and prevent any confusion. If he tries to return, the HK authorities will confiscate his passport