If vegapunk die end of the arc , not problem at all.
Currently , still it is not problem . Because , if somebody make explanation about how to create these df , they need to know techniques or methods . This is very ridiculous. What do you expect for explanation. There is two way . One is this . Experimental observation for a long time and other way , vegapunk needs to know everything about ancient history. Please make a suggestion for better way. Do we need to learn after luffy found out one piece ? Basically , all of things are produced and created by science with unlimited energy sources. That is easy .