Clinton should not drop out of the race just because Bernie Sanders appears to have a lead in the California primary. Bernie Sanders barely held his own in the caucuses, Hillary Clinton certainly is not going to drop out because he seems to have a lead in the California primary.
If Bernie Sanders wins in the California primary Hillary Clinton will still have more delegates than he does. The race will be more tedious for her but she will still be able to edge him out due to the amount of super delegates she has already had commit to her. It really is a done deal. Bernie is only an annoying thorn in her side.
Hillary Clinton has lead the Democratic race up to this point, and with her super delegates, she continues to dominate Sanders. It would be absurd for her to drop out of the race just before officially landing the nomination. She has earned her delegates, and will turn out to be the nominee and most likely our next president.
Despite Bernie Sanders' win in the California primary, Clinton still has the advantage over him. She is the presidential candidate of the establishment and has more support among Congress and the House of Representatives. She also still has the lead in delegates and has the majority of superdelegates saying they will vote for her.