The single greatest fear I have with the agencies and freelancers that I work with is that they’ll leave.
Of the many companies I’ve worked with over the years I think I could name every single person who worked on my projects but I doubt I could name every agency. These were people I worked with day-in day-out for years and when they went it was hard to build up that same bond with their successors.
Sadly agencies often don’t make this easy for themselves.