What is the test for substituting jurors for a jury in a civil case when a juror dies or becomes ill?

Pursuant to Penal Code section 1089, "[i]f at any time, whether before or after the final submission of the case to the jury, a juror dies or becomes ill, or upon other good cause shown to the court is found to be unable to perform his or her duty, . . . the court may order the juror to be discharged and draw the name of an alternate, who shall then take a place in the jury box, and be subject to the same rules and regulations as though the alternate juror had been selected as one of the original jurors." This process for substituting jurors "preserves the essential features of the jury trial required by the Sixth Amendment and due process clause of the Fourteenth Amendment." (People v. Bowers (2001) 87 Cal.App.4th 722, 729.)