That's kind of a shoddy way of doing things, since you could interrupt Barney's path at any time and the whole sequence would screw up. Fortunately, scripted_sequences have a property that allows you to trigger another entity after it's finished its sequence. Use this to trigger a multi_manager that opens your door and, a second later, triggers the other scripted_sequence for Barney to walk off to. Quite simple, really.
...I have way too much time on my hands.