Hard to tell but I would be worried too. It could suffer from oxygen defficiency and eventually get root rot but it probably depends on how much the small roots near the "old" top are affected (the ones that usually grow around 4" deep). Those small roots are the ones where the plant absorbs water and they are now 12" deep.

Normally, one plants the shrub leveled with the ground or (better yet) slightly higher than the surrounding soil. But now that it is an additional 8" under the surrounding soil, water could collect there and cause problems if it does not drain quickly. The weight of the soil could make it hard to breathe.

If you want to play it safe, you can always transplant it back into the same spot such that it is higher. You may need to prune it or manually disentangle the stems to do this.

Luis