Fresh back from a few weeks off, and I found my mailbox jammed with letters from folks responding to my "Yes (and No)" column presaging the Yes concert at Artpark. That piece pondered the significance (or lack thereof) of bands who continue to trade beneath the same brand name even after hugely influential original members were no longer involved.

The response regarding Yes was pretty much an even split. Half of you felt that the band needed to continue, with or without the man whose vocal fingerprint played such an important role in defining its sound, the inimitable (though many try) Jon Anderson. The other half seemed to take the idea of Yes sans Anderson as a personal insult. Both responses make perfect sense, frustratingly.

Russel, writing from Sydney, Australia, recalled seeing Yes with Anderson's replacement, Jon Davison, at the State Theatre in Sydney back in January. "I didn't miss Jon Anderson one bit," he insists.

Steve from Oakfield, N.Y., said he would attend the Artpark show "to see Chris (Squire) play bass," but added "I've seen Yes 8 times. This one won't count. The other 8 times, Jon Anderson was the singer."

Mike from Buffalo, a Yes fan since 1971, boycotted the Artpark show. "For me," he wrote, "they have fallen too far, like a great sports figure that stayed [around] way too long."

Interesting thoughts, all. I attended the Artpark show and was frankly floored by the performance. It must be admitted that I was on vacation, and not wearing my critic's hat, but was instead fully enjoying the show as an enthusiastic fan of long standing. That said, Davison blew me away. He sang effortlessly and gracefully, he inhabited the songs and avoided mere imitation, and he nailed every single note.

The rest of the band played with fire and conviction, and the song selection -- despite an early end brought about by a looming electrical storm that seemed to have guitarist Steve Howe quaking in his boots -- was ambitious and awesome. I'd see Yes with Davison again tomorrow, given the opportunity.

This is not always the case with bands that lose key members and insist on carrying on. Often, it's tempting to view what they do as a mere cash-grab for nostalgia and mortgage payment's sake.

But perhaps the greatest example of a musical ensemble continuing to create relevant music after losing a core member involves the Grateful Dead. Wednesday would have been the late Jerry Garcia's 70th birthday, and even though those who have fallen under Garcia's musical spell over the years don't need much in the way of urging, it seemed that the guitarist, vocalist and spiritual cornerstone of the Dead was on everyone's minds even more than usual these past few weeks.

The Grateful Dead ended when Garcia died. But interestingly, Grateful Dead music did not. The various offshoots from the surviving members -- among them, the Other Ones, Ratdog, Phil & Friends, Rhythm Devils, the Dead and Furthur -- have carried the music forward in the wake of Garcia's passing, mostly in a positive and forward-looking manner.

This is the best-case scenario when a band loses a pivotal member -- the spirit of that member's contribution to the music is celebrated, and the music itself takes on a protean form, ever shifting and accommodating the influences of the various musicians passing through the ranks.

For the Grateful Dead, this has meant incorporating the Garcia spirit -- searching, questioning, improvising, forcing the music into real-time, locating formulas and then challenging them -- into a sound that has continued to evolve without his corporeal input.

One of the most exciting developments in this area involves GD drummer Billy Kreutzmann and his relatively new outfit, 7 Walkers. In this instance, the Garcia spirit of improvisation has been married to America's deepest and perhaps most rich sound, the music of New Orleans.

7 Walkers finds Kreutzmann joining with New Orleans roots musician supreme Papa Mali, Funky Meters bassist George Porter Jr. and Grateful Dead lyricist Robert Hunter, among others, in service of a sound that picks up where Dead "second line" jams like "Aiko Aiko" and "Hey Pocky Way" left off. It's natural, organic, deeply inspired. And over it all looms the shadow of the man who would have been 70 this week.

It's fitting that Garcia's birthday will be celebrated in Buffalo by the debut area performance of 7 Walkers when the band performs at 8 p.m. Saturday in the Tralf Music Hall (622 Main St.).

Afterward, Garcia's music will continue to be celebrated with the official after-party in Duke's Bohemian Grove Bar (253 Allen St.), with Funktional Flow and Sonic Garden and Friends handling the honors beginning at 11 p.m.

So it seems that bands can indeed survive significant lineup changes, if their hearts are in the right place.