It all depends on how their contract with the client is structured. I believe there are some contracts that have bonus tiers built-in if a certain percentage of shops are completed within a given timeframe. Perhaps there are bonuses for completing all assignments as well.
Technically, a client could claim breach of contract for any misses by the MSC, but, baring any extraneous circumstances, I doubt legal action would be pursued.
Missing too many contractual requirements, over time, could certainly lead to the client looking elsewhere for their MSC partner options...
"We're just two lost souls swimming in a fish bowl -- year after year..."