My personal pespective of having cancer and going to Burning Man:
I finished my radiation treatments the Friday before we left for the playa on Sunday. No chemo luckily, and brachytherapy rather than external radiation. Breast cancer btw, lumpectomy not a full mastectomy. I also have asthma and a bad hernia from a totally different surgery. I did fine, lots of painkillers as needed, stayed out of the sun, was waited on hand and foot by hubby and niece, slept lots, stayed hydrated, dust masks, and spent two long afternoons early in the week in the cooled tents at Totem. I also was hauled around on a four wheeled bike so I rarely needed to walk or balance unless I felt up to it.
I would have felt far, far worse if I had stayed home. Yes I was weak and had to take it easy; I had to depend on others to do the hard physical stuff in camp, but being on the playa did me good. Not precisely radical self-reliance, but arrangements had been made. I never felt the need to go to medical at all. My incisions from the brachytherapy actually healed up very well in the heat and dry conditions. Could I party all night? No. Did I drink alcohol? No. Did I care? No. Did I have a most excellent time? Yes.
Your friend should only consider the trip if he can get a superb and reliable support team in place to help him over any rough patches. He should expect a low-key burn, emotional, have a bail out plan in place. This is when sacrifices are made, both on his part and on the part of the people who support him. If everyone is on board, then this is entirely possible. If he wants to party full on, that may not be possible, nor fair to those who have decided to help him. That's my opinion as I do not know your friend at all, you'll have to ask him about his expectations of himself, the event, and his friends. Then plan accordingly.
Cancer changes everything.
Some sunshine, some dust, a little paint and a tutu. Yeah.