As a head coach and a defensive coordinator, Vrabel's teams have run basically the same defensive scheme, a lot of zone, with a bend, don't break mentality. It's who Vrabel is as he doesn't want his team to give up the big play and wants to force offenses to have to slowly move down the field.
So no, I don't see the overall scheme changing much no matter what personnel is on the defensive side of the ball. As Vrabel himself said today, nothing is really going to change and retaining Bowen demonstrates that the defensive scheme will be very much the same as last season. Why else would Bowen, someone who has followed Vrabel at all of his coaching stops, be retained?
Will there be some adjustments, I'm sure there will be as Bowen has a year under his belt and hopefully is more comfortable calling plays. But I still expect to see the corners playing nearly 10 yards off and a lot of 4 man rushes. It's what Vrabel scheme is. Keeping the scheme the same tells me that they think the personnel from last season weren't executing the defense well enough. And to be honest, there is evidence to suggest that there were communication issues on the field.
It's why I hope that the Titans invest heavily in their defensive line and Bowen learns to rotate some of the key defensive players so as not to wear them out by the middle of the season (Landry and Simmons come to mind). Upgrade the pass rush and some of the weaknesses of the scheme will be less of a factor.