Rabastan wasn't expecting a lot of detail, not really. He didn't need to be fully briefed on what Barty was doing; it was better that they were each doing different things and passing any information to each other only when necessary.
It just made him feel better to say something, however briefly, to know that things were being done to find his niece. He had assumed that Barty would make the case a high priority, considering who Vera was related to; the Lestranges had certainly earned the right to be granted first priority for a family matter like this, even when there were concerns like Potter to worry about. And not only that, but they were friends; Rabastan would have done the same if the roles were reversed.
"Good," was all he said, and then managed a smile. With that established, he didn't mind being distracted for a little while, and he was in good company. "So what did I miss, this time? You've usually got at least one juicy bit of news for me."