For example let's break down these numbers: 7,362,490 Californians voted for Hilary in 2016 and 3,916,209 for Trump with a record 75.3% turnout. Let's up that to 7,500,000 Dems and 4,000,000 Reps for simplicity.
Split amongst Cox and Allen is 2,000,000 votes each. If each of the four top Democrats receives the exact same amount of votes then each Dem will only have 1,875,000 votes each resulting in two Republicans facing off in the general election.
Democrats would need 500,000 new voters to break even, assuming votes are split equally. But for their best case scenario assuming 100% turnout AND a 2% increase in the total voting population who all vote Democrat gives us 9,973,094 Democratic voters, which split four ways is 2,493,274 votes per candidate, but the CA GOP would only have to increase their total voters by 1,000,000 in order to take the two top spits. However, if turnout returns to the 2014 primary level then only about 30% of eligible voters will participate meaning only about 3,000,000 voters total, which is about 1,800,000 Democrats and 1,200,000 Republicans. If Dems split four ways then they'd only get 450,000 votes per candidate while Republicans get 600,000 votes for their two candidates.
So again the CA GOP could eek out a long shot victory from this, but it all depends the division within CA Dems > division within CA Reps. Are there 600,000-2,000,000 people willing to vote for Chaing or Eastin? I doubt it but there's no way to know for certain because everyone will get a ballot with no information about the candidates. If people just choose based on hearsay or what they see on Twitter, anything could happen because each of the four Dems have some sort of non-liberal element or position about them that the media will exaggerate.
(disclaimer: not that it would be change much since the CA GOP are hardcore cucks especially Cox and Allen. Never forget that.)