Media critics disagree on whether the passing of Friends -- coupled with next week's departure of Frasier -- signals the start of a mass-sitcom extinction or merely the latest ebb in the history of one of TV's most durable genres.

But few disagree that Friends will be a hard act to follow, leaving a gaping hole to fill in NBC's prime-time schedule and challenging network executives to find the next breakout comedy hit to replace it.

In the meantime, General Electric Co.-owned NBC is hyping the Friends send-off for all its worth and cashing in on the huge audience likely to tune in for the event.

Some 40 million to 50 million viewers are expected to watch the six coffee-sipping pals bid their final farewell, eager to learn whether Ross and Rachel, the show's star-crossed lovers played by David Schwimmer and Jennifer Aniston, end up just Friends or in each other's arms. The conventional wisdom is that producers wouldn't dare let those two go it alone.

The off-and-on Rachel-Ross romance has remained one of the show's underpinnings and rivals the most storied affairs in prime-time history, ranking up there with Sam and Diane from "Cheers" and George Clooney and Julianna Margulies on "ER."

"What's really astounding to watch is how NBC and its allied industries have managed to turn this, in essence, into a secular holiday," said Robert Thompson, head of Syracuse University's Center for the Study of Popular Television.

The anticipation is so great that the hour-long Friends finale is commanding sold-out, Super Bowl-sized advertising rates averaging $2 million for 30 seconds of commercial time, the most ever for a sitcom. The Seinfeldswan song held the previous record at $1.7 million.

"It will be one of the highest-rated programs of the year. It will be an event that will dominate conversations among Americans," said Tim Spengler, the top network TV buyer for New York-based media buying and planning agency Initiative. "The opportunity for brands to associate with that kind of platform is harder than ever to find."

Not since NBC's celebrated Jerry Seinfeld sitcom "show about nothing" exited the airwaves six years ago has there been so much hoopla surrounding the conclusion of a TV show.

NBC is devoting three full hours of its Thursday schedule to the Friends farewell -- a one-hour retrospective followed by the final episode itself and capped with a special edition of "The Tonight Show with Jay Leno" reuniting the six co-stars on the set of the Friends Central Perk cafe.

Friends viewing parties are being organized by local NBC affiliates around the country, including an event co-hosted by Clear Channel Communications, the NBC-owned Los Angeles station and the network's future corporate partner, Vivendi Universal, at Universal CityWalk featuring a special broadcast of the finale on a giant outdoor Astrovision screen.

Since "Seinfeld" signed off in 1998, Friends has reigned as the comic centerpiece of NBC's formidable Thursday night lineup billed as "Must-See-TV." The Emmy-winning series still ranks as the most-watched comedy, and the No. 5 prime time show this season, averaging about 20 million viewers per week.

Debuting in the fall of 1994, Friends and its cast of winsome, easygoing singles unfettered by mortgages and kids quickly caught on with viewers looking for an escape from the stressed-out '90s. Along the way the show has made household names of its six principal characters -- Schwimmer, Aniston, Courteney Cox Arquette (Monica), Matthew Perry (Chandler), Lisa Kudrow (Phoebe) and Matt LeBlanc (Joey).