Why does this not expand to inexpensive programs that haven't been previously funded, but could be? I've read that we can save lives for a handful of dollars per life in Africa with greater access to medical care, mosquito nets, antimalarial drugs, etc.

If getting rid of existing affordable aid is murder, why is failing to render new affordable aid not? Doesn't this inherently place an incentivization mechanism and inherent preference for the old ways of doing things, when newer ways can be more efficient and save more lives with fewer dollars?

The short answer is that removing the aid you were previously providing is more morally salient than not helping in the first place.

Short answers aside, could you stop with the indirection? The original question was whether millions of people could die due to funding cuts. The answer is yes, regardless of your moral views about how you should spend your own money.