That’s unfortunate, but it’s no cause for panic. You can accomplish more than you think through cross-training. Forget the rower, but do use your indoor bike and treadmill to continue with the plan in this alternative modality. I’d use the bike for Z3-5 stuff and walking for everything else, as it will help preserve the impact tolerance of your lower extremity tissues. After the two weeks, give yourself one week to “build a bridge” back to the 100km plan. Start with a test run and then make each subsequent day’s training look a little more like the planned training until the two paths merge. You’ve got this!