Even if you had the very best experts that knew COBOL and some “modern” language, along with all the right competent supporting staff (documentation, analysts, qa, ops) AND they had skilled, experienced and competent management overseeing it, doing something like that in months is just probably very, very difficult, if not impossible.

If you look back over the respected literature (which means sidestep the hot-take Youtube techfluencers going gaga over rather pedestrian things in languages and tools and frameworks and so on - these dingalings are typically so far up their own rear-ends and likely to just make the same old mistakes already documented in books like Mythical Man-Month and many probably won’t read it because they think it’s about older systems, therefore irrelevant.) I doubt you’d find much support for a claim that it could be done.