Dylan McDermott, 39, and Lara Flynn Boyle, 30, won’t be filing for unemployment anytime soon. ABC ratings champ “The Practice” will remain on the air through spring 2004, at least, its network announced this weekend. Speaking before a conference of TV writers, ABC execs also said they had no fear about the aging of the their audience, though, in something of a pre-emptive move, they are going to bring youthful rock and pop stars onto “Who Wants to Be a Millionaire” starting next month. In addition, starting in March, ABC will attempt some crossover episodes involving “The Practice” and “Gideon’s Crossing,” a struggling medical drama, which, like the legal drama, is set in Boston, said network entertainment chief Stu Bloomberg. Meanwhile, over at NBC, “Tonight” show host Jay Leno, 50, will be keeping people awake though the end of 2005, at least. In negotiations that were said to have last 20 minutes, Leno closed a new deal with the network, details of which were not reported. Coincidentally, the first term of George W. Bush — a frequent target of Leno’s humor — will be drawing to a close in 2005, too.