OK, I'm having problems with the maths here but it seems to me that you don't have any possibility of having the required number of days to qualify. Any days before 13 April 2008 have been lost. That would make it about 450 days (ish) that you have towards the RO.
Also, the inability to work (medically retired) as far as I can see from what you have said so far, has not prevented you from physically returning to Canada before your PR card expired. The tax returns are of no consequence as far as I am aware. I suspect that you will have difficulty demonstrating a humanitarian defence if they decide to revoke PR status.
Your best bet is to enter via a land border from the USA and see what happens, if that is possible for you. If you need to apply for a Travel Document, you are looking at a hard battle.