How is it "mercenary?" Tons of TV series write out cast members and bring in new ones, especially in these serialized times. And if Cavanaugh knew going in that he was only onboard for one year, that would've given him and his agent plenty of advance notice to line up other work. Indeed, sometimes actors are only interested in signing up for a finite term on a series -- Christopher Eccleston on Doctor Who, say.
Producers are mercenary and actors are whores.
If he's told, sure. Everything is copacetic. If they don't tell Tom as they watch the guy sign into a a mortgage for a 16 million dollar beach house, then they're scum.
Christopher Eccleston is a perfect example because he was not told he was going to be asked to shove it. It has since then become public knowledge that David Tenant was chosen to be his replacement before Chris was picked a transitional Doctor. It was all rather sketchy.
Eccleston is bitter and angry, and given the right sort of hallpass, would burn Cardiff Studios to the ground.