It depends on how heavy the losses are, especially the loss of landing craft and air transport. These were in short supply in every theatre of war and it took until '44 for the WA to get enough of them together for Overlord. Assault troops wouldn't be a problem. The WA had plenty of 2d and 3d wave divisions ready to deploy, some of whom had more experience and training in amphibious ops than the initial assault divisions. IMO the big loss would be to the specially trained commando/ranger, parachute, and glider units which play a very important role in any amphibious invasion. Unlike the first wave units, very few of these highly trained soldiers would escape Overlord and the WA would be hard pressed to find replacements. The UK had another airborne division and, if Dragoon doesn't kick off, the WA could press gang the ad-hoc 1st Airborne Task Force into service. The WA would still be one abn div short for an Overlord-sized invasion. Also if Dragoon doesn't go, the WA could maybe break up the 1st Special Service Force, which had many veterans of the 1st, 3d, and 4th Ranger Battlions for commando operations.
If Overlord failed, It would be a while before the Allies could launch a similarly large and complex operation. However, they could continue to invade the perhipery of Europe (Norway, Southern Europe, Balkans) and continue to drain the Axis. IMO, though, I don't see Overlord failing. A well planned and well supported amphibious invasion is all but impossible to beat off, and the WA were at top of their game at Normandy.