inspiration taken from the 'Once and Future' comic series perhaps? pretty much this exact thing happens in it. it's quite short and finished, highly recommend it!
Is the definition of English as a “French-German creole” (or even a romance-germanic creole) at all mainstream in linguistics? I was under the impression that mainstream linguistics classifies modern English firmly as West Germanic, and discounts the Normans’ infusion of French vocabulary into it as inconsequential.
My headcanon theory is indeed that English is a creole language.
Mix the grammar, verbes and functional words of the lower-status people (natives, imported slaves) and nouns of the higher-status people (invaders, colonizers and masters) and boom, after a few generations you get a creole language.
This theory works surprisingly as well for English as for, for example, Caribbean creoles.