Which disease is more fatal: chronic bronchitis or chronic kidney disease (stage 4)?

Depends on severity. Neither disease is fatal if they are stable. However, stage 4 kidney disease tends to worsen to stage 5 disease which can be fatal. The worsening bronchitis depends on the cause (for example, common bacterial infection versus TB or not receiving the right antibiotics). Kidney disease is more likely than bronchitis to worsen without good compliance with medicines and diet and is more serious.