If your ex-husband has MRSA that is usually curable with an IV antibiotic called vancomycin. If your ex has VRS or vancomycin resistant staph that is much more severe. Both of these are usually worse if there is another problem going on that would compermise his immune system in some way. (I am just guessing he is a young healthy man otherwise, this is a huge + on his side)
My son at 2 weeks old had gotten system wide staph because he had a bladder malformation and ended up getting toxic shock syndrome from it. They were sure he was going to die and later on I found out that he had less than a 4% chance to live...and he is here and WONDERUL!!
My point is that keep a positive attitude, miracles happen everyday. Why shouldn't the next one be for your ex! If he is doing well now that is great since people with worsening infections go down hill very rapidly within the hour even.
Unfortunatly there is really no prep to do in case the worst does happen. Why prep your daughter for somthing that "might" happen...it will only scare her. If things go downhill you will know it as the medical staff will let you know to prepare that he will not make it. Don't rely on the internet, his medical team are much more in tune with what his current status is than any website stats are.
Good luck and here's to a speedy recovery!