Well, yeah, that's the simplified to the point of absurdity math.
For an exact number for that question I'm not sure how to even go about it. It won't only be BMR that affects the total calorie count, there are multiple other factors as well. Some systemic and some all the way down to cellular.
JISSN | Full text | Metabolic adaptation to weight loss: implications for the athlete: "Interestingly, the decline in TDEE often exceeds the magnitude predicted by the loss of body mass. Previous literature refers to this excessive drop in TDEE as adaptive thermogenesis, and suggests that it functions to promote the restoration of baseline body weight [13-15]. Adaptive thermogenesis may help to partially explain the increasing difficulty experienced when weight loss plateaus despite low caloric intake, and the common propensity to regain weight after weight loss." and "To avoid rapid fat gain following the cessation of a diet, ?reverse dieting? has also become popular among physique athletes. Such a process involves slowly increasing caloric intake in a stepwise fashion. In theory, providing a small caloric surplus might help to restore circulating hormone levels and energy expenditure toward pre-diet values, while closely matching energy intake to the recovering metabolic rate in an effort to reduce fat accretion. Ideally, such a process would eventually restore circulating hormones and metabolic rate to baseline levels while avoiding rapid fat gain. While anecdotal reports of successful reverse dieting have led to an increase in its popularity, research is needed to evaluate its efficacy."
He's studying weight loss in athletes... but that's an interesting little paper. And it would be similar processes.
I don't know. I'm not sure if there is a formula for that. But I have to assume that it would stabilize at some meager %age of total body fat and take at least half a year to plateau. The endochrine works slowly and you're not really talking about a huge amount (200 is a lot, but still it's really not THAT much. It'll be less than a 10% difference for a man below middle age). But what the fuck do I know. I might be retarded.