I am in a similar situation. I'm running chicago at the end of october and I'm injured right now. I ran a 23 miler last week in 2:26 and was feeling on top of the world. But, as things usually go, The injury totally sidetracked me. I ran 8 today but it hurt so now I'm going to have to take at least a week off. Here is the good news for people like us: If you've been doing your training on schedule and been good on all your long runs so far then you're ready already and you can basicly stop practicing for a month and not see any real decline in performance come race day.
I would suggest to you that you maybe swim in the pool or use the bike just so you don't experience withdraw problems. It's strange but when a runner needs to take a break they will experience actually physical problems due to not keeping up the routine. You will become irritable, maybe not sleep well, get small aches and pains in your knees and hips and back, and any other myriad of problems. So, to relieve these issues you should continue to do some sort of exercise just so you keep yourself sane. Other than that you won't have a problem on race day. Assuming you've healed completely, you won't see any drop-off even if you take off from now untill race day.
I read a long time ago about an olympic marathoner who got put in the hospital for some non running related issue a month before the olympics. He was in for three weeks and got released like a week and a half before the race. All he could do was a few miles a day up untill race day. Turns out he ran a
PR when the race came. I'm sorry that I can't remember which athlete it was, but I believe I read it durring the Barcelona Games. It's what coaches have been saying forever. If you've done everything, then you can coast the last month and no problem.
Hope that helps