I don't know much about bulldogs, but I bred pugs for about 6 years.
Dog gestation is approximately 63 days; this is not exact and you do not know to the day when the pups will arrive. I have seen them come as many as five days early or 3 days late. Also, if the stud has had unsupervised access to the the bitch you may have missed seeing the first tie and therefore not calculate the date accurately. There is a temperature-taking technique you can use to predict dog labor, however, which is fairly (but not perfectly) reliable. You should be able to google it; basically, the mother's temperature drops 24-48 hours before labor begins.
Placentas do detach earlier in dogs than in humans. I have seen puppies die due to premature detachment. However, I think it is exaggeration to say that the placenta usually detaches before birth, or that several pups' placentas detach at the same time. It is normal to have an hour between births, and that is too long for the pup to survive with a detached placenta. Frequently the placenta does not detach until after the pup has emerged (the weight of the pup usually detaches it at this point, but not always).
I have seen a few cases where a pup got "stuck" and took a long time to birth. We were lucky, and in all of these cases the mother was eventually able to birth the pup; but it was usually stillborn. The following pup was stillborn in about half these cases, probably due to placental detachment. Subsequent pups were fine. This is hardly scientific evidence, though, just my experience.
Also, it is not true that a dog can't communicate when things don't "feel right". However, someone who has never helped a dog whelp before may have a hard time telling the difference between normal labor discomfort and a problem.
Another thing to bear in mind is that a c-section is just as traumatic for a dog as for a human. This trauma, and the post-op discomfort, does increase the likelihood that a bitch will reject her puppies. This is not very likely, but if it happens it can be a big problem - they do make formula for pupppies, but it is not nearly as close to dog-breastmilk as human formula is to human-breastmilk (not that I'm a fan of formula for humans).
I don't think attempting a natural birth would be certain death for your dog, but there would be some risk, especially to the pups. On the other hand, there are significant downsides to a c-section. I think that if I were in your situation, I would attempt a natural birth if there was a nearby 24-hour clinic you could go to if she had problems, and if you could have someone experienced with whelping come over to assist you during the labor - someone who will know how to spot the danger signs. You could do the trial of labor in the vet's office (if your vet is willing) but it would be best to do it at home - being in a strange location can panic your dog and stall or complicate labor.
If you choose to c-section, you may want to wait until she shows signs of being about to go into labor - that way you can be sure the pups are ready to be born.
One thing you should think about when deciding is what your priorities are. If your dog's comfort is your top priority, I would lean toward trying natural birth, especially if you plan to breed her again. If 100% pup survival is your top priority, I would go for the c-section. And whatever you choose, get as educated as you can about dog pregnancy, whelping and caring for newborn pups.
