I've faced a species of this issue myself.  But it turns out that the answer to this question involves more potential twists and turns than one might first believe.  Seems there's more than one way to skin this headless cat.  And, in a most interesting twist, the appellate division tackling this question is very same division that decided Parris v. Superior Court, 109 Cal. App. 4th 285 (2003) [pre-certification communications with class members], Belaire-West Landscape, Inc. v. Superior Court, 149 Cal. App. 4th 554 (2007) [discovery of putative class member identity and contact information], and Lee v. Dynamex, Inc., 166 Cal. App. 4th 1325 (2008) [discovery of putative class member identity and contact information], so one might say that this division has a certain expertise regarding this prickly area.

In Pirjada v. Superior Court (December 12, 2011), the Court of Appeal (Second Appellate District, Division Seven) issued an order to show cause but ultimately denied the petition for a writ of mandate brought by the plaintiff following the denial of a discovery motion.  The plaintiff settled his individual claim through direct negotiations with defendant's CEO.  The trial court granted leave to amend the complaint to name a new class representative but denied the motion to compel precertification discovery to identify a suitable class representative.

What will ultimately happen in this case remains unclear.  But this opinion does identify key decisions that might have changed the result, though that is hard to say with certainty.

The Court began its discussion by restating existing standards.  First, class member rights are protected, even pre-certification.  Second, court approval is not needed to communicate with putative class members, but when a court's assistance is solicited, a court can consider the potential for abuse.  Third, class member contact information is "generally discoverable."  Fourth, lead plaintiffs, who are unqualified to serve as a class representative may, "in a proper case," move for discovery to find a new representative.  However, the Court also noted that precertification discovery is not a matter of absolute right.

Next, citing La Sala v. American Savings & Loan Assn., 5 Cal. 3d 864  (1971) and Kagan v. Gibraltar Sav. & Loan Assn., 35 Cal. 3d 582 (1984) (disapproved in part on another ground in Meyer v. Sprint Spectrum L.P., 45 Cal.4th 634 (2009)), the Court emphasized the trial court's obligation, as also stated in Rule 3.770, to consider carefully any request to dismiss a class action and evaluate whether notice is necessary.

Then, after noting that the standard of review is the abuse of discretion standard, the Court explained why the writ must be denied. Petitioner first argued, as a matter of discovery law, that because defendant failed to respond to document requests, it waived any objection. Absent a finding that the failure was the result of mistake, inadvertence or excusable neglect, Petitioner argued that it was an abuse of discretion to deny the motion to compel. Second, as a matter of the procedural law governing class actions, Petitioner argued that the court abused its discretion in declining to authorize notice to potential class members about the need for a substitute representative. The Court found the first contention to be incorrect and the second premature.

Interestingly, though the Court ultimately rejected the challenge to the discovery order, it was highly critical of defendant's behavior:

Outside the context of representative and class actions it may well be, as Pacific National observes, “a matter of common knowledge and common sense” that once a plaintiff settles his or her case any discovery responses not yet due no longer need to be served. Because the lawsuit against Pacific National was filed as a class action, however, and the individual settlement with Pirjada was made without the participation or consent of his lawyer, the experienced employment law attorneys representing Pacific National should have either objected to the still-outstanding discovery as moot, moved for a protective order or taken steps to ensure that the settlement agreement between their client and Pirjada included a provision withdrawing any remaining discovery requests.

Slip op., at 12.  The Court then observed that the trial court could have crafted a number of alternative orders designed to locate a suitable representative.  Here's where things get interesting.  The trial court first considered and denied a motion to give notice to the class.  That order was not challenged, though the Court telegraphed its opinion of the Order:

Although the court's decision to deny Westrup Klick's motion for notice to the class was based largely on a distinction between consumer and employee class actions, a distinction we implicitly rejected in Belaire-West Landscape, Inc. v. Superior Court, supra, 149 Cal.App.4th 554, the propriety of that ruling is not before us. Westrup Klick did not seek writ review of the court's May 26, 2011 order. Instead, it elected to proceed by way of a motion to compel.

Slip op., at 13.  The Court then concluded that the trial court's decision to deny the motion to compel after giving time to find a new representative was not arbitrary or capricious.

As to the second, premature argument, the Court also seemed to be hinting that the trial court should proceed with caution:

Whether or not the superior court's initial decision not to notify potential class members that Pirjada now lacks standing to represent the class was correct, the court will necessarily revisit that question when it hears its order to show cause regarding dismissal. Counsel's declaration in support of the petition for writ of mandate indicates a new class representative cannot be identified by the informal means authorized in Parris, supra, 109 Cal.App.4th 285, and discussed by the superior court during the May 26, 2011 hearing. Assuming that remains the case, Westrup Klick will have an opportunity to demonstrate to the court that some form of notice is required to avoid prejudice to absent class members. It would be inappropriate for us to prejudge the outcome of that hearing or to restrict the superior court's discretion by attempting to outline the factors it should weigh in deciding how to comply with the requirements of La Sala, Kagan and Rule 3.770.

Slip op., at 14-15.  Riiiiiight.  Good thing they didn't give the trial court a look at their cards.

So now you know, at a minimum, that when the representative suddenly hits the eject button, class counsel needs to walk carefully through the dismissal process so as to seek the best possible methods for locating replacement representatives and/or obtaining notice to the putative class.