The majority of recent immigrants are from eastern Europe, and they are definitely not tee-total. The asian population, and their second and third generation British born descendents have been here for decades, so that does not account for closures now. I know of a few asians who do go to the pub.
There have been many pub closures in my town and I don't think any can be attributed to immigration even though we have a Bangladeshi community and have had a recent influx of Poles.
The reason is a change in society. When I go the pubs, the majority of customers are over 45. Younger people are less interested than they were. There is a lot more to interest young people than there were 30 years ago. You can pay half the price for alcohol in Supermarkets so a lot drink at home. The home has changed as well, it is also a cinema, a games centre, disco or library, there are more reasons to keep you in.