1
general::
Phrase(s): run its course
[for something] to continue through its cycle of existence, especially a disease. • Sorry. There is no medicine for it. It will just have to run its course.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Proceed to its logical or natural conclusion, as in The doctor said the cold would probably run its course within a week. This idiom employs course in the sense of "an onward movement in a particular path." [Second half of 1500s]
American Heritage Idioms