Yes, Sarah, I think a Sanders-Warren ticket is a possibility. But it's also key to remember that while Sanders and Warren have a lot in common ideologically, she is also very much an establishment Democrat (she did, after all, endorse Clinton over Sanders in 2016). I could see big figures in the party pushing her to endorse Biden. Of course, there's no love lost personally between Warren and Biden (goes way back to a bankruptcy bill long before she was a senator) so perhaps she'd rather not fall in with him. It's a legitimately knotty situation for her, I think.