In reply to Paul Troon:
Ah that's unlucky. I'm pretty sure you will be able to run a half marathon by then, if you let it heal and follow a good physio's advice. Will you be at your best? Probably not.
So, if you're just aiming to turn up and get round (e.g. slowly or run/walk), then I'd be hopeful some good physio will get you to the start line. If you're aiming to beat your PB or push yourself as hard as you can, then maybe forget about that!
Note that my experience of this kind of thing is a tiny calf tear (like someone shot me in the leg) not grade 2 hamstring tear. It really depends on the extent of your injury, but I wouldn't write yourself off yet...see how the physio goes. Good luck!