Yes, unless you have reason to distrust your brother, let him handle things. You don't have to do anything, it doesn't sound like.
Nobody has been diagnosed with anything yet. And even people with cirrhosis can live for years and years, in some cases. Remember my second husband? Diagnosed with early cirrhosis and still drinking like a fish? Still alive and apparently not dependent on family, and it's been 17 years since his near-death experience and subsequent diagnosis.
Don't future-trip. Your dad may be around for a long time, however bad he looks.