Returning to work. Is there a common experience?

Is there any kind of common thread or expectation about returning to work? I am a High School History teacher, teaching everything from Ancient World to Ap classes in European and American studies as well as a bit of Philosophy. I have a reputation of working well with dificult students and so am rewarded by being given all the difficult students. I love the job tho'it is very stressfull and exhausting. I'm also an English expat, been living in the US since 1999.

So, A little history.

1st May 2013 started urinating blood. Consulted Doctor who found a lump on my kidney (why does no one use the word tumour?). By the end of the month they had removed the tumour and part of the vein. Surgery was long and I lost a lot of blood spent most of June in Hospital at the University of Maryland Medical Centre. Naturally, it being summer there was no work: good job because I was out of my mind on pain killers!

Diagnosed with stage IV metastatic renal cell carcinoma, I started a course of IL2 in August 2013 (one week on, one week off, one week on, 6 weeks recovery). Scan showed retreat in my tumours by about fifty %. I started my second round of IL2 in October with what my oncologist has called catastrophic near-fatal results, infected blood, pleurisy, colitus (in both colons) pneumonia. I was in the ICU and Cancer ward from the begining of October to thanksgiving. I had to learn to walk before I could leave.

I never felt that I had fully recovered from the surgery, and was naivly surprised how it effected the whole body. Coming home from the IL2 treatment was a chanllenge. I had daily physical herapy. I started walking, first with a walker and then with a cane, which I still use. Walking to the end of the driveway, then the end of the road, then round the block. Currently I take the dog for a walk of about a mile.

I returned to work, working half a day, in March and continued in that vein until the end of the school year in June.

With the new school year in August, I went back full time. I managed 1 full week. I worked four days the next week and was finished: unable to walk or work - its not unusual for a teacher to cover 10 miles walking in a working day. I started working 4 days  a week, taking wednesday off.

This worked until I started stutent in September (37.5 Two weeks on , one week off). The inevitable diahrrea stopped me from getting to work reliably in the morning, I am now working half days again 5 days a week.

My Principal wants to know how long this is likely to last. I cant answer because I've never been in this position before.

Human resources want rid of me for taking too much time off sick. That much of that time was spent on the cusp of life and death is of no interest to them.

Naturally, all my sick pay is gone and my 1/2 income is being covered by the local sick bank from a one time only 'chonic and catastrophic' fund that runs out an june 2015

Is this experience familiar to anyone?

Any advice, re emloyment or finance?