Super delegates total 715. To get the nomination based on pledged delegates alone, a candidate would have to get 59% of the pledged delegates (a pledged delegate lead of 2383 to 1667, which is 716 pledged delegates).

Kentucky & Oregon contests are on May 17 and then there is a gap until June 4. The June contests are worth a total of 781 delegates. To clinch the nomination before June using pledged delegates would require a 2383 to 886 pledged delegate lead of 1497.

You really cannot think of things in terms of needing to be able to get to 2383 based on pledged delegates. To drop out based on that idea basically would never happen unless someone is getting utterly destroyed.

What matters is the types of percentages Sanders would have to win by to catch up in pledged delegates. After calling Clinton's win in Arizona but before calling Utah or Idaho, John King gave Sanders wins in every single remaining state (including Utah and Idaho) at a percentage of 55%/45%. Clinton still had a sizeable pledged delegate lead. Why? Because even after winning Idaho & Utah by larger margins last night, Clinton has won 57% of pledged delegates so far.

To win the nomination, Sanders needs to have his own area of the country that runs up delegates for him in a way that the south ran up delegates for Clinton plus win New York, Pennsylvania, and California to offset her non-south wins. While Sanders will likely have similar performances in the middle of the country (like Wyoming, Montana, and the Dakotas) & the pacific northwest as Clinton did in the south, that won't be enough. They have too low of a population to offset her southern delegates.

Because of that, the race is effectively over.