He must live a regular life, ortherwise he will fall ill.是并列句，不是复合句。即：He must live a regular life, ortherwise he will fall ill.是 He must live a regular life + ortherwise（表示选择关系的并列连词） + he will fall ill；而Unless he lives a regular life, he will fall ill.是含有条件状语从句的主从复合句，Unless he lives a regular life是条件状语从句, he will fall ill是主句，不是复杂句。
