With respect to a certain poster on this thread living in a foreign country, I don't think they can accurately speak to the testing and experiences here in the US, whatever the case in their home country. Accordingly, I would put little reliance on the opinion offered.
In theory, I'm a breeder. A diagnosis of Mareks would mean destroying my whole flock, disinfecting, waiting a year, then starting over. Because I'm a breeder - there is no commercial value in selling Mareks exposed chicks.
I'm an NPIP participant in FL. A diagnosis of MG means the State would destroy my flock.
These are easy decisions for me, because of the "business" I'm in - risks I accepted when I decided to sell birds (potentially).
That said, if you are willing to maintain a closed flock, and have no interest in selling (or donating) birds to friends and neighbors, plenty of people happily maintain flocks which carry Mareks and/or have been exposed to MG, no (significant) difference from any other backyard flock once the disease(s) take the weakest/most susceptible members.
Whether or not to continue under those circumstances, or to sanitize, pause, and start over, is a decision only you can make.