Much of Berwick St was at one point scheduled for serious redevelopment, which would have neccesitated getting rid of MVE and Sister Ray. However, I haven't heard much about it for a while now, so maybe that threat has passed. However, the more generalised threat of high rent increases isn't going to go away. Also, as everyone says, the internet has more or less made second hand record stores redundant (or at least cut their profit margins so that they have to be MUCH leaner operations).
As regards MVE, it's seems to have an unerring ability to remain afloat despite really bad business mismanagement over many years. It's demise has been predicted for so long that, peversely, I'm sure it'll be around for years. However, their margins are going to get worse and worse and worse, I think- it was about 30% of selling price a couple of years ago, now it's heading down to 20% and it'll get even less. Soon, it'd even be worth paying someone to stick it on eBay for you!