The festival will move on to Colorado next year without its founder, the late Robert Redford. The Sundance Film Festival may be a little bittersweet this year. It will be familiar in some ways as it kicks off on Thursday in Park City, Utah. There will be stars, from Natalie Portman to Charli XCX, and breakout discoveries, tearjerkers, comedies, thrillers, oddities that defy categorization and maybe even a few future Oscar nominees. The pop ups and sponsors will be out in full force on Main Street. The lines to get into the 90 movies premiering across 10 days will be long and the volunteers will be endlessly helpful and cheery in subfreezing temperatures.But the country’s premier showcase for independent film is also in a time of profound transition after decades of relative stability. The festival is bidding farewell to its longtime home and forging forward without its founder, Robert Redford, who died in September. Next year, it must find its footing in another mountain town, Boulder, Colorado.