> Being invaluable to the team gives you negotiating leverage.

A firm I know fired their lasts Perl developer, purely to cut costs. Their payments system was written in Perl. When it stopped working, they asked my friend to step in.

He refused, said management should take responsebility for their decisions, and his manager got all pissy. Soon my friend left the firm too. The management is still earning bonuses and promotions. Nobody cares.