I think the issue here is that neither group can really take the other on. The death eaters aren't likely to take the necessary steps to take over the government properly and they can't win in an open war. However, there is very little way for any muggles to pick out wizards in a crowd so as soon as any attempted plan goes south, they could pull back into obscurity and try again. Granted the muggles might be significantly more prepared at that point, but I don't know if you can defeat a group of wizards who are properly prepared to counter muggles.