Hi Jenny,
As John suggests, you will get a lot of different advice and the bottom line is that there are many different factors which will influence the healing process for you as an individual. My experience after a herniated disc and 3 x cortisone injections has been that you can recover and run again. I had (2/3yrs ago) typical sciatica, leg weakness and usual associated aches and pains, and all of these do still flare up occassionally now and again depending on what I have been doing, still using painkillers as and when.
You will get to know what activities you can and can't do, and in my experience running is generally beneficial for recovery from this injury, but you do need to be honest and acknowledge when your body is telling you to have a rest. For me it is the less obvious things like gardening, painting/decorating and sitting for too long that are most likely to cause it to flare up.
I believe the most important thing is to remain positive and have patience, there will always be another great north run if this year is not meant for you. You will get better, and you will adapt, don't force your recovery, run when you feel ok, don't when you are in pain, and you will find you will have more opportunities to run than not as time goes by. I think stretching (when you are not in pain) is hugely beneficial after a run so would encourage you to keep doing that. I have completed about 12 marathons since having the cortisone etc, and there are still days when I dont run because of back pain. As John said above, listen to your body, it is an amazing piece of kit and you will get a lot from it, if treated with respect. A lot of people have a lot of opinions on this topic, most of these mascarading as fact, with no supporting evidence. Keep an open mind, be optimistic, have patience, but above all enjoy your running.
Good luck