In terms of manpower losses would be rough but far from crippling somewhere in the region of 70-90,000 men killed and captured, losses in heavy equipment would be limited by the fact that the Germans could not manage to get heavy equipment across apart from maybe (maybe) 200 or so tanks, no field guns or heavier pieces for example, few trucks and next to no horse drawn vehicles.
Assuming a launch sometime in late 1940 it is unlikely to really delay the redeployment eastward by much.
It will add to the losses in barges which will have economic ramifications. It will be a huge loss of face internationally.
It is very unlikely to lead to a coup though. Even with losses to the Kriegsmarine and Luftwaffe thrown in casualties so far in the war are going to look exceptionally cheap to a ruling class and generals inured to the level of hardship of the 1st World War.
At worst the entire Kriegsmarine is dismissed as incompetent but unlikely that most would even think to blame Hitler.