Former Sox GM Theo Epstein is gone but not forgotten. The new president of baseball ops for the Chicago Cubs got a warm reception this weekend at the Brighton Music Hall, where he was one of several familiar faces helping Buffalo Tom celebrate its 25th anniversary. Friday night, BT’s Bill Janovitz, Chris Colbourn, and Tom Maginnis were joined by Lexington-bred comedian Eugene Mirman, Ted Leo, Fuzzy’s Chris Toppin and Hilken Mancini, Belly’s Tanya Donelly, Mike Gent of the Figgs, Mike O’Malley, and Dinosaur Jr.’s J Mascis, whose guitar added an exquisite squeal to a cover of Neil Young’s “Cortez the Killer.’’ (Urge Overkill’s Nash Kato was also in the crowd, as were “Leftovers’’ author Tom Perrotta and his wife, writer Mary Granfield.) Saturday, after attending his 20th high school reunion in Brookline, Epstein stopped by to play guitar on BuffTom’s cover of the Who’s “The Seeker,’’ with O’Malley singing - and to kibitz about the Cubs with former Volcano Suns bassist Bob Weston, who lives in Chicago these days. Also making the scene over the weekend were keyboardist Phil Aiken, Mean Creek’s Chris Keene and Aurore Ounjian, Daddy’s Junky Music’s Mike Tocker, and actor Lance Greene.