it depends on the person and the case. Some people are able to face it stronger than others. Personally I think people say what they think they would do....but when it comes to it, you just really don't knwo what your reaction is.
personnally, being as realistic as i can be....i think i would act differently in the beginning....but learn about the illness more in depth, and learn to see what they need and what they don't need. It's difficult, some people want to act as if nothings wrong....but others don't. I would respect my friend and go with the flow.
I hate it when people overreact to it.....i mean....if YOU overreact, how do you think they would feel? They don't NEED more pressure from you....they have enough anxiety on their own and from their own family. I'd give them the space they wanted....but still be around just in case. Then go with the flow =)
One thing i would never do is abandon them.
Btw, with your list of illnesses, SARS is kinda different.....it's easily passed on so....for health reasons you would HAVE to be protected. I don't know it's tough, but I think i would learn to adapt quickly.