Dear @Nima,
Good to hear from you again and thank you for your question.
Your friend did very well and I am glad he has a very supportive employer, too! The so-called "Beschäftigungsduldung" is an important step and often a struggle. After holding the Beschäftigungsduldung for 30 months, he can apply for a residence permit according to section 25b (6) of the German Residence Act. It is still a long way, but after holding the residence permit for 5 years, he may apply for the permanent residence (Niederlassungserlaubnis). My colleague explained the process here as well.
In any case, please don't hesitate to get back to us with any further questions.
All the best,
Meike