As John says, slowing to .78 from .8 is no big event ATC wise, and if it lasts long enough so that you cannot 'compensate' later to keep waypoint ETAs within limits, you just tell ATC and issue revised ETAs. They will let you know if that creates a problem and if it is that bumpy, in all probability everyone else is doing the same. The faster you hit the bumps the greater the airfame loading, as he says. Not really a 'structural risk' as such, just common sense.