I am in curious time right now. 16 days to the marathon, so the running plan is definitely in taper mode. The usual plan is to cut the miles, but maintain the intensity. My last two weeks of training have been compromised by going to Italy (pasta, house, heat, wine, mozzarella di bufala, hills, time..) and a knee problem that seems to come on at mile 3. So, I have missed my last big long run and the one before that wasn't perfect.
I've read enough to know that the right approach is not to panic, most people rarely hit 80% of their plan, and I do have a lot of the fitness banked. And on the day I will be able to manage, it feels like this is in the category of 'painful but not damaging'. However this stage of training is all about the mind - trusting in the work completed, relying on years of experience that says your muscles need 3 weeks to feel fresh, and knowing that you cannot 'cram' the training now, even if your knee was fine - which is isn't.
So, a balancing act. Come the day, all will be well.