China and Russia dumping dollars

Read some articles indicating China and Russia are dumping the dollar. I mean I heard we owe the Chinese something like 7 trillion in debt. Given the U. S. Government refuses to restrain spending, are we now reaching the point where countries like China will simply cut off the credit line, and then dump the dollar. I'm no economist by far, but I always understood that having the dollar as the World Reserve Currency [WRC] meant countries like China [and Russia] bought dollars and that action propped up our dollar.

I always believed [right or wrong] that countries would never dump the dollar as the WRC, since the shock of that happening would throw the whole world monetary system into a tail spin.

Anybody can enlighten me on this?

Should I deversify into precious metals [Gold or Silver]?