IMO, this is not a case of "self defense"....
The clerk did not (apparently) use "deadly force", or force that would normally be considered to be deadly force by a reasonable person.
"Use of force" is not the same as "deadly force". Many statutes make clear distinctions. New York law specifies "physical force" and then makes clear distinction between "physical force" and subsets, or "degrees" of physical force, including the specific subset "deadly physical force". Obviously this is not New York but the same legal standard exists in some form or another in most places.
So, IMO, this is not a case of the clerk using "deadly physical force". The clerk used reasonable physical force to prevent a robbery. The perpetrator placed themselves in a condition and situation where a normal, healthy person would have survived with little, probably no, injury but a situation in which their self-induced condition led to death.
This is no more a "Self defense" incident than when a drunk runs a red light, gets T-boned by someone with the green and ends up dead. Self-induced fatality at someone elses hands.
Suicide by store clerk.
Still happily answering to the call-sign Peetza.
The problem, as you so eloquently put it, is choice.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.