I'm sure that every time you went to work it was like running a marathon. We all hold on for as long as we can and most likely do a lot of damage to our health in the process (I know I did). I also think it is common to feel "if only I had made that extra last effort, I could have prevented this from happening". However every time you went to work, I'll bet you WERE putting in that extra effort.
In a nutshell, you have done your absolute best and you need to recognise this...not beat yourself up over it.
I'm so sorry this has happened to you and hope that some how you can obtain financial support.