i'm gonna ignore the obvious fact that 'killing' them will do absolutely nothing.
didn't i already entertain this option by saying 'what if he and bill gates pooled their money'? did you not read that part? there's like 10 words in this post, how could you miss that?
you would need ALL of the money of the 2 richest people in the world EVERY YEAR. so, this year it would be 2 people, then next year it would be 3, then it would require 4 or 5 or 6, etc. you would run out billionaires pretty quickly.
this is even an extremely optimistic calculation, because as you probably know, most of that wealth is tied up in assets, meaning they would have to be liquidated first, and quickly. let me ask you: have you ever been to a business which had to liquidate their assets quickly? that's called a fire sale, and usually the sale percentages are very high. so probably you will be very lucky indeed if you can recuperate 50% of the accounting value of these assets.
the rebuttal is (obviously) that thinking random individuals should shoulder this burden firstly shows a keen misunderstanding of what it would take to actually make that happen, not to mention the nature of the problem, and secondly an embarrassing display of ignorance about how the people actually involved in trying to end world hunger (i.e. the people writing the UN reports, not the ones writing the low-effort articles) want it to come about, namely via combined government action. that would not only be more coherent legally, it would also be more sustainable.