The magic of the wall still holds. The wall was made with magic and non-magical means, so even if the magic from the wall was somehow destroyed or made obsolete, the power of the wall remains. Magic can be transferred from objects so if the magic was removed from one part of the wall it could always be transferred to another part.
Also, even if the magic of wall was gone, the wall is still massive and regarded as a major barrier for the White Walkers. Even the sense of a barrier for the White Walkers is enough to keep them at bay.
