The ball is still considered to be in the backcourt until the ball bounces in the frontcourt or hits a player who is considered to be in the frontcourt. Note that if a player is in the air and sails across the midcourt line but his feet last touched the backcourt, he is not considered to be in the frontcourt until his feet touch the ground in the frontcourt. It doesn't matter where the ball passed the midcourt line in the air.
If a team calls a timeout before 10 seconds has expired and hasn't gotten the ball across midcourt, the 10 second count starts over but the shot clock doesn't when play resumes. The 10 second count doesn't start until a player gains control on a rebound or touches the ball on a throw in.
Another misunderstood part of the rule is a player in possession of the ball can get a foot across the line and even dribble the ball in the frontcourt, but if he still has a foot in the backcourt, he is considered to be in the backcourt. All 3 points have to be in the frontcourt: both feet and the ball. If the player is dribbling the ball and only 2 of those things are across and one isn't he is considered to be in the backcourt.
Only 1 of those 3 things have to be in the backcourt for a backcourt violation to occur after the play has moved to the frontcourt (e.g. foot touches the midcourt line).