A most troubling announcement from Syracuse chamber-pop band Ra Ra Riot passed through my Facebook feed. It read, in all lowercase, "sad to say, allie is leaving the band…" There, beneath an oversaturated Polaroid, was cellist/backing vocalist Alexandra Lawn's amicable message: "not a 'goodbye.'"

Bands change members all the time; I get this. As a critic and music lover, I wonder about the shifting sound and dynamics, the old songs versus the new, unwritten ones. Particularly when that sound has intrinsic melody, like Lawn's cello, stitched into it.

Take NYC math-rockers Battles. Their instrumental avant-jams didn't really combust the hipster populace's trainers until Warp Records LP Mirrored—and specifically the single "Atlas," with Tyondai Braxton's helium-treated croon. Yet when Braxton left the band in summer of 2010, Battles' machinelike precision and groove-inducing stage presence only grew.

Cali art-rock provocateurs Xiu Xiu were a rotating cast around tortured soul Jamie Stewart for years. But multi-instrumentalist Caralee McElroy's entry in 2004 was a balm to Stewart's harsh delivery (witness the sweet, McElroy-sung track "Hello From Eau Claire"). Her departure after five years left me bewildered, beginning with "who is going to play all her gear?!" Enter Angela Seo, plugging into the crackling synths of New Wave horrorfestDear God, I Hate Myself (replete with a notorious, vomitious video). I'm relieved to say that Xiu Xiu are heavy as ever, if pounding new track "Hi" is any indication.

East Coast synth-vampires Cold Cave may have originated as "just" a solo effort by dark god Wesley Eisold, but by debut Love Came Close he'd added noisician Dominick "Prurient" Fernow and McElroy—plus created a scorching live act. Though McElroy left before second LP, Cherish the Light Years (taking the sweeter pop sounds with her), the addition of Alex Garcia-Rivera (who drummed with Eisold in Boston hardcore group Give Up the Ghost) kept Cold Cave's live sound at a bracing, post-apocalyptic froth.

But what if the change doesn't groove well? Or, more complicatedly, it alters my feelings as a fan? I'll come clean: I credit my initial openness to Ra Ra Riot to Lawn. Usually she played honeyed counterpoint to Wes Miles' bright tenor. But she sang lead on the jazz-inflected torchsong "You And I Know," sounding like she just took a slug of scotch and a three-second cigarette drag. So as I await and listen for Ra Ra Riot this year, I'm crossing my fingers for a future Alexandra Lawn solo.

Image: Alexandra Lawn (and Ra Ra Riot) at Bowery Ballroom, September 22, 2010. Courtesy the author.