Should he take a loan from his boss to do Hajj?

Praise be to Allah.

We ask Allaah to reward this boss greatly, and to make more people like this among the Muslims, people who make things easy for the Muslims and help them to obey Allaah. 

Your Hajj done in this manner is valid and there is nothing wrong with it if you are able to pay off the installments from your salary. But if your salary is not enough to pay off the installments without delay, or it may lead to you not having enough to spend on the people under your care, then it is better to delay Hajj until Allaah makes it easy for you. 

Shaykh Ibn Baaz (may Allaah have mercy on him) was asked about a person who takes a loan in order to do Hajj. He replied: 

There is nothing wrong with that if he is able to pay it off. 

Fataawa Ibn Baaz, 16/393 

The half of the expenses that your boss pays is regarded as a gift, so there is nothing wrong with accepting it and doing Hajj with it.  See question no. 36990 

And Allaah knows best.