The correct answer to this open question is the following.
Although there are no options included, we can say the following.
What happened to the missions when the Franciscan priests left was that the government secularized most of the buildings and properties that belonged to this priest from the Catholic Church.
The term secularize means that religious activities and property passed from the church to the civil society or a laic institution.
The beginning of the 1800s represented the end of the Franciscan presence in the North American missions. When Mexico gained the Revolutionary War of Independence against the Spaniards, most frays and priests were expelled from California, Arizona, New Mexico, and Texas. Just a few frays stayed in parts of California to continue their evangelization work.