The guilt can manifest itself in different ways. I lost my mom to cancer 2 years ago. We lived 4 hours apart.
She was declared terminal about 5 months before she passed. When she went to the hospital for the last time and then to hospice, that time spanned 6 weeks -- we thought it would be a week to 10 days.
The point of this is this: I have a job, and at the time, my wife was 7-8 months pregnant. Not knowing when she would pass, I eventually had to lengthen the time between visits for the month she was in hospice. I only had so much sick time at work (plus, when I'm not at work, someone has to cover for me), and again, the pregnant wife. She passed on a 3 day off stretch, but I was using that to try to put baby furniture together (as we were behind time-wise) instead of visiting. Everyday I wish I had gone home to see her that weekend. When I got the call she was near the end, I couldn't get there fast enough, and she passed while I was on the interstate.
Different, but similar. Don't beat yourself up. There was no neglect or anything like that... things just happen. I was 40 when she died, and my daughter was born 34 days later. The one thing I learned? It's never easy to lose your mom -- at any age.