But all of that is assuming that the airports you mention all rely solely on airline pax revenue. I would suggest that diversity is the key to a strong future.
Ive posted elsewhere that DSA is a highly unlikely choice for LS. Its from the horses mouth too, so to speak... Easyjet would be great for DSA, it aint gonna happen though. TOM will continue to increase/decrease their movements and offerings in line with the fickle trends of pax. FR will not return to HUY but they will be running summer only routes from DSA and DTV excluding DUB.
Returning back to the thread topic though. I dont think there is much else for airports like HUY and DTV to do except clutch at straws. Just look at other airports this size, most that have had significant growth rely largely on one airline for that. All it takes is one successful airline.... May never happen but you never know when things look up.