After the impaneling of the jury and before verdict, the court may discharge a juror upon a showing of the juror’s sickness, a serious illness or death of a member of the juror’s immediate family, an undue hardship, an extreme inconvenience, any other inability to perform the juror’s duty or a public necessity. Alternate jurors, in the order in which they were selected, shall replace jurors who become unable or disqualified to perform their duties. If an alternate juror is required to replace a regular juror after the jury has retired to deliberate, the court shall recall the jury, seat the alternate and resubmit the case to the jury. If no alternate juror has been selected, the trial may proceed with the remaining jurors, only if the parties so agree. If the parties do not so agree, the jury shall be discharged, and a new jury then or afterwards impaneled.