I'm a great one for scraping the dregs of the mix from the bowl with a spatula, i.e. jogging round a marathon after a longest run of 18 miles - walk/run - a week or two before. But that is still pretty tough the last few miles, even with a good few gels and decent rest, and starting off healthy.
It really sucks being injured (I spent nearly a year after my first marathon doing the physio rounds) so I do feel for you, believe me!
It just sounds like too big an ask though. If you'd had a month off and been healthy before...
If you can't get refunds on hotel etc, go anyway, do the breakfast run, spectate, have fun, watch other people screw up and then... Whatever they did, don't do it in Berlin!
Meanwhile, enjoy the enforced rest by trying out other stuff - if you've ever fancied parachute jumping, now is surely a good time because it's not like a twisted ankle is going to put a spoke in your running(!). Life is too short not to squeeze the most out of it...scuba diving? Water polo?