Forget about business process execution languages and belocolus "business process engines" that will protect you from all harm.
Your problems do not stem from the lack of a silver bullet syntax or the lack of a killer programming language feature. Your problems lie in two fundamental concepts that need to be central to how you think about business processes in a distributed world - (a) event driven execution and (b) temporal decoupling.
Without those, all the WF*, BP*, WS* and *ML's in the world cannot help you.
More on this line of thought in this week's ITWorld aricle : When modelling business processes, upside down is the right way up.