Rot is basically a fungal attack on the wood, feeding on the starches in the fibres. So, once the fungus is there, with the spores, then it's there. Progressively the fungus weakens the integrity of the wood until its structure collapses. Products such as cuprinol 5 star simple arrest the attack by killing the fungi, and effectively making the wood poisonous to future attacks where treated. However, most treatments these days are water soluble, and will eventually wash out. So technically you can stabilise the situation. All rot fungi need water - but sometimes very little % moisture in the wood is necessary, and some nasties, such as dry rot, can fetch water via sending out very long strands to find it from a considerable distance away. Of course natural resins and oils help against rot because of repelling water. Rot is a whole subject in itself - just google dry rot and its an education!