I've worked multiple elections in California. During the last election, here's how this was handled in my county: In the event you didn't get your absentee ballot in the mail, you could show up at your polling place and let them know you never got it. They will have your mail in ballot nullified (just in case it does show up) and you are allowed to vote in person. The purpose of nullifying your mail in ballot is to prevent a person from voting twice, purposefully or accidentally, and to prevent an unauthorized recipient from turning in your ballot.

Again, that's how it worked in my county during the last election. I have no idea what's going to happen this election, but I expect it to be a proper clusterfuck.