Partir would be to leave or depart(usually a specific place) whereas sortir is more like to go out or exit, typically used in describing the action rather than focusing on the destination. It's kind of a bizarre difference it would seem to an English speaker. Think of the difference between exiting the grocery store versus leaving Paris. departing to or from a place = partir exit, go out of, run out of = sortir
You may not have heard it 1bimic, but it is still correct English.
part - definition of part by the Free Online Dictionary, Thesaurus and ... www.thefreedictionary.com/part
- To break up (a relationship) by separating the elements involved: parted company.
Example - We cannot live together, so we are going to part. (separate - leave each other)
This is not used as much as it used to be, but is correct.