As a survival server, MCAU has a number of protections in place to prevent unwanted destruction of player builds and the environment. By default, explosions and fire ticks are disabled on the server, which prevents mobs like Creepers from damaging the environment or builds. TNT is also disabled as a result of this.
However, while these protections are in place, this does not stop players from actually destroying blocks that are not protected by regioning. It is a players responsibility to region their builds and projects to prevent unwanted potential griefing by other players. Griefing in general, when done maliciously, is not permitted on MCAU and players found doing so can and will be issued with a ban, as well as being branded as such.
Griefing that is considered accidental are viewed on a case by case basis.
If a player feels they have been griefed, the player needs to lodge a Mod Request at the location of the griefing. Staff will attend to the situation when they are available. Generally, griefing can be rolled back, so long as there is a log of it. However, while Staff will try their best to get things back to how they were, it is not guaranteed everything can be restored.
In the case that you have been banned due to griefing, check out the appeals page.