I don't think it is possible for a tightly seated lid on a plastic fermentor to leak around the O-ring, Period. Even for a lid placed gently on the top of a bucket the airlock poses a static fluid resistance of about 0.06 psi while the weight of the lid alone would require about 0.20 psi to move enough to vent the pressure. So, because higher pressure gasses seek lower pressure areas through the path of least resistance it should never leak from under the lid. This assumes that the o-ring isn't damaged, the o-ring is fixed to the lid correctly and the lid is not warped in any way. Now if your krausen takes up the head space that's a totally different story...
As far as re-pitching, I wouldn't either... I agree to wait until your hydrometer arrives then test the gravity against the estimated Og. No bubbles doesn't always mean no magic. In the future, with dry yeast, I would try making a starter with DME. Wait to see bubbles and a krausen forming on that, then pitch. I can help you determine if you could have a problem before brewing and save money. If you have to trash something it will be the yeast and not the entire kit.