Question

Should Muslims leave work during the last ten days of Ramadan? 
May Allah reward you. 

Answer: 

In the Name of Allah the Most Gracious, the Most Merciful. May Allah's Blessings and Peace be upon our Master Muhammad, the Faithful and the Honest. 

Dear noble brother/sister
As-Salamu Alaikom wa Rahmatu Allah wa Barakatoh 

To answer your question, I would like to mention these pieces of information: 

First: In Shari'ah rulings there are categories; Fard (obligation), Wajib (duty), Istihsan (recommended), Mubah (neutral), Makruh Tanzihan (it is a detested matter in Shari'ah without the promise of punishment if performed), Makruk Tahriman (it is a command for abstinence that has been established by a speculative proof (dalil dhanni). It is closer to the unlawful (haram) and can also be defined as being in diametrical opposition to a Wajib), and Muharram (unlawful). 

Second: All matters are categorized according to this system of Shari'ah rulings. 

Third:  The matter of I'tikaf (is an Islamic practice consisting of a period of staying in a Masjid for a certain number of days, devoting oneself to Ibadah during these days and staying away from worldly affairs.) in Ramadan. 

It is not Fard nor is it Wajib, but it is Sunnah. Thus, if you are a person with unlimited income, and you do not have to be at work on these days (the last ten days of Ramadan), you can observe I'tikaf. As for the employee, what should he do? Well, Allah the Almighty never burdens a person beyond his scope. Hence, whoever has a job from which he makes a living, cannot observe I'tikaf. However, there is what we may call a divided I'tikaf.

Can you not pray Qiyaam al-Lail (the night prayer)? For example, you can wake up an hour before dawn to pray and read the Quran, which is a kind of I'tikaf. Do you not pray Taraweeh in congregation? This is also a kind of I'tikaf. 

Accordingly, you can observe a continuous I'tikaf if you are well-off, and you do not have to go to work every day, and you can observe a divided I'tikaf in Ramadan within the scope of your capacity. In fact, religion makes things easy to Muslims, and Allah the Almighty never burdens a person beyond his scope. Obligatory matters in religion are the obligations, while the mandatory matters are required from whoever can perform them, not from all people.