It’s dangerous, and could be expensive, if a traveller uses on outback track when it’s officially closed. The authorities will close a track if, due to heavy rain, the track has become impassible and/or use of the track would cause damaging wheel ruts to be created.
Checking the sign on leaving Marree tells us that all tracks are open and that we can continue to William Creek.
lookANDsee 
We did a tyre on the road to Marree when we were them a few years ago, but they were well equipped to deal with tyres if not much else.