I've been a Parisian all my life, except a few years in the US and Canada. I have many American and Canadian friends in Paris. Quite a few of them have settled in France very fine without speaking French at all at first. It's mostly a matter of finding the job that requires you to work mostly in English (it's easy).
Most of them ended up speaking fluent French after 2-3 years, mostly after having taken French lessons, because they wanted to. A minority has chosen to remain ignorant of the culture they live in, and can barely utter some basic sentences in French after spending 15+ years there. Worse, their spoken english has impoverished and become a strange sabir. They still are very happy Parisians, even though I feel they miss a lot, and I find it a little sad.