After successfully building a machine language version of thePascal compiler, one could in principle discard the P-code interpreter andthe P-code version of the compiler. Why might one choose not to do so?

Pascal is a high-level programming language, and anyone can decide to write a machine language compiler with it, If Pascal language specifications get to change or somewhere in the code a bug is discovered, it will be easier to build the machine language compiler again from the Pascal code version than deciding to modify the machine language.