In the finale of the Tony-winning musical “Avenue Q,” the verse that usually elicits the biggest reaction is one reminding the audience that everything in life is temporary by providing three ephemeral examples: sex, your hair and George Bush.

Turns out, the lyricists were right. Mr. Bush is, as the song goes, “only for now.” So what happens to the line after the 43rd president leaves office next month?

“We still don’t know, is the truth of it, we’re not really sure what to do,” said the show’s co-writer, Robert Lopez, who along with Jeff Marx won the 2004 Tony for best original score. “When we wrote it back in 2001, we thought of that problem but, being reasonable people, we figured, ‘Well, if we have that problem, that’s the dream problem to have.’ It’s good that we’re dealing with it now.”

Indeed, the show, with its cast of humans and Sesame Street-style puppets contending with unemployment, racism and homosexuality, was a surprise Broadway hit that few expected would take off as it had, let alone outlast Mr. Bush.

“Avenue Q” won best musical in 2004 and is presently the 25th longest-running show in Broadway history and climbing. It’s also spawned a national tour, a London company, a soon-to-debut Australia company and productions that have performed from Stockholm to Manila, always with the Bush joke intact.

One answer not under consideration: Barack Obama.

“I certainly don’t feel the same way about him as I did about Bush,” Mr. Lopez said. “We’re not advocating Barack Obama in that line.”

The show’s book writer, Jeff Whitty, explained it wouldn’t work anyway because “it doesn’t fit the music’s rhythm.”

Also, “for whatever reason, it’s not funny,” Mr. Whitty said, echoing the complaints of some comedians about Obama as a punch line. “I think it’s because he’s too new. If he turns out to be a terrible president, then maybe it would work, I suppose.”

Mr. Lopez said he wrote in Mr. Bush’s name at the start of his presidency because he was angered by the bitter 2000 Florida recount. “We were feeling a little depressed about it and put that in there to remind us that he was only temporary,” Mr. Lopez said.

Early on in the show’s run, when Mr. Bush’s popularity was at its peak, the apparent slam on the current president was viewed as somewhat taboo and risky, Mr. Whitty said. It even turned off some audience members “who told us they loved the show up until that moment,” he said.

Mr. Whitty and Mr. Marx said they have several ideas to solve the problem but they will likely open the matter in coming weeks to a public contest via the show’s Web site, AvenueQ.com. The contest’s rules are being crafted.

Mr. Lopez is resigned that the new line may never have the surprise and thrill factor of the original.