Does a Muslim have to relinquish the nationality of his disbelieving country and depart from it after converting to Islam?

A Muslim is not obligated to renounce his infidel nationality, but his loyalty must be to Allah, His Messenger, and the believers. As for emigration from the lands of disbelief, it becomes obligatory if a Muslim fears for his religion and cannot practice its rituals openly. It is recommended if he is able to practice its rituals openly and does not fear persecution, unless his stay there serves a benefit for Muslims.