It depends how good you are at getting straight back on the wagon. Last year I decided to have a treat for my birthday, and never did as well at being strict afterwards. Personally, if you can, I would recommend finding a different way to celebrate your birthday that doesn't involve food, or if it does that it is low carb. But it's up to you, and some people can successfully just have that one day and get straight back on. Be honest with yourself, will you go back with the same enthusiasm as when you started?
The first time on a vlcd before you come off the wagon is by far the easiest (in my opinion), so I would think really seriously about coming off it!