"Keep applying and talking to companies even after you have started negotiations" YES. Do not stop until your first day (half kidding). One time I stopped in

"Keep applying and talking to companies even after you have started negotiations" YES. Do not stop until your first day (half kidding). One time I stopped interviewing after accepting an offer...only to find out there were rounds of reference checks (and one of them didn't go well). It was 2-3 weeks of anxious bullshit, but only because I already turned down everything else that was in motion. Who knows maybe a second company will come through with a better offer.