Even at 100% code coverage it is possible to have missed many code paths that involve nonlocal control flow. The most common issue here would be exceptions in languages that support it. In most operating systems there are various interrupts that a program can also encounter (e.g., a lovely SEGFAULT in many *nix type operating systems) and other operating system and hardware level issues (like OOM killer in Linux or an NMI or ECC memory error in embedded systems).

So, 100% code coverage may not even be enough for some applications as was discussed in another too level thread (medical device) or other hard to fix (spacecraft) or life-threatening situations.