The deformity reminds me of bilateral cleft lip and/or palette as seen in humans. I believe it to be a congenital anomaly which will not "regrow". Since the duck has grown and thrived after all he's been through, why not give him a chance. I think he will be fine and possibly one of your best babies.
	
		
			
		
		
	
				
			
	
	
	
	
	
	
	
	