I'm sorry about your mother. It's important to know we were there for our parents, and have no regrets about their final hours. My father passed away the first year I was working, and I do regret not being able to be there as much as I would have liked.
When my ds was the same age as yours, I went to university three or four days a week, from about 8 until 5 (with travel times). I never left any pumped milk, and he was not getting formula or any other kind of mammal/soy/alternative milk. He just ate, drank water, and nursed more when I was around. I never had any problems with supply on the days I was home (he could nurse at any time, and seemed satisfied after); and he often would nurse instead of eating food on my days off. However, I we did cosleep and I think he nursed A LOT at night. If you have a child that actually SLEEPS at night, and want to keep it that way, you might need to be more careful of his daytime milk intake.