Again, without knowing how many restaurants OPENED, the mere number of closures is meaningless.
300 restaurants close in NYC every year, easy. Probably double that. Same thing for LA, or Chicago, or Miami- somewhere, there are probably closure rates per capita per year, based on business licence studies.
just tossing out a number, like 350, doesnt tell you if BA is any different from any other world city its size.
To figure out whether the economy is getting worse, or this is just normal churn, you would need more info.