This is an old but sad story: a plaintiff in federal court misses the expert disclosure deadline and then the entire case is lost. The district court has the authority to set deadlines for expert disclosure and can enforce those deadlines. After the plaintiffs failed to disclose an expert, the district court entered summary judgment against them. They appealed, but the Seventh Circuit was also unsympathetic.
Source: HASSEBROCK v. BERNHOFT, Court of Appeals, 7th Circuit 2016 – Google Scholar