That would be התפרקה (broke up) or התפצלה (split up). With נפרדה I’d expect it to split up from something else, like, הקבוצה התפצלה\נפרדה מהקבוצה הגדולה יותר.
Second this. פרד is used as 'break up' (sexual relationship) or in a more mundane 'to part' as in, we went to a movie and then parted ways. When speaking about a group ceasing to be, פרק would be the way to go