Can you leave China for vacations during work time frame in China?

My husband is an American citizen with valid 10 year multiple entry L to China. He has use it twice already for short trips to visit me. Now he wants to work in China to stay with me long term. According to your article, he can apply for a Z in US, assuming he finds an employer will hire him for 5 years, enter China, and get the resident permit for 5 years. During the 5 years, if we want to leave China to travel or visit families in US, can he enter and exit China using his existing L? or what else can he use? because the Z will be voided when he enter china