First, I hope your husband is in remission and has a long future ahead of him. That's scary.
This is a band-aid fix and not a permanent solution, but sometimes when something is scary what kids need is security first. Last summer I was seriously injured and hospitalized for two weeks. When I got out I was bedridden for three months, and since my home is not wheelchair accessible (and I couldn't care for my kids, then 4 and 20 months) we had to relocate to my parents' home. While my kids were being cared for by loving grandparents, my daughter still had terrible anxiety from the whole thing. After the first month or so she was able to lie in the bed with me to go to sleep, and that improved her anxiety a lot. Even now if she is upset and feeling anxious, I can always get her to go to sleep by lying with her in my bed, even if she knows I'm not staying after she's asleep.
As awful as this time is for you, it is even scarier for your son. If it's possible, you might find it a lot easier to allow him to sleep with you for a while. Another sure-fire way to knock out my daughter is to have her lie on the sofa and listen to an iPod (she has a kids' one, so the headphones fit). Just being able to SEE us helps her, and I'm still able to do whatever I do in the evenings. I figure there's time enough to reorganize her sleeping, and what's most important right now is that everyone SLEEP, and that your son feel secure.
Best of luck to you.