Does a ceramic coating stop working when it stops beading?

No. Beading is only one visible sign of surface hydrophobicity and is not a complete measure of coating condition. In many cases only the coating's water-repellent top surface has been masked or worn, while the protective layer itself is still bonded to the paint. A coating may still provide chemical resistance, easier cleaning and lower surface energy even when a thin layer of contamination has reduced visible beading. Judge the coating on several signs together: how easily dirt releases during a wash, how slick the paint feels when clean, and how water behaves after decontamination rather than before it.