(This needs updating for final nodes.)

A Dag is finished when:

1: There are no nodes remaining to submit, all post scripts have completed, the final node has completed.
1: No nodes are queued up and the ready queue is empty.  This implies a cycle in the putative DAG or that something internally in DAGMan is messed up. DAGMan should exit, writing out a rescue DAG.
1: A node has exited with failure and all remaining nodes have a dependency on it completing successfully.  DAGMan should exit, writing out a rescue DAG.