Options for someone who didn't take Math Subject GRE
I'd recommend applying anyway, with an explanation of why you didn't take the exam.  Not having a math GRE score could hurt your application, but at many schools it won't conclusively rule it out.  (You can always ask the school in advance whether they will consider your application under these circumstances.  I'd bet they say yes.)  Assuming the self-assessment in your question is accurate, you should be a strong candidate for graduate school, and I don't think a missing GRE score would derail everything given that you have a compelling excuse.