depends….
They may have a backup of your records stored off site, wouldn’t bank on it though. Mind you unless you’ve got a particular treatment plan going on currently, it’s not going to be a massive issue, any dentist will be able to do an exam on your teeth to get a picture of what’s going on.
They should have a business continuity plan under the regulations, or contact your local PCT to find out what they doing with all the patients.
Re records, although it’s a NHS dentist it’s probably run by an independent private company, so won’t have records stored on a “central NHS database” AFAIK, you could ask for your FP17s (claims made by your dentist about work done to your teeth) from the BSA, but I wouldn’t think that was really neccessary