Agency world is notorious re customer loyalty.. with a major account worth up to 40% of a company's revenue is a dangerous game. However, government contracts would in normal economy be a 'safe bet', like tories & Saatchi for example.
But I think the biggest challenge is when Private Equity gets involved, esp. not cash flow industries like marketing/agency world (compare to cash & carry/banking etc.)
good luck to those guys at I-level.