When is a Resignation a Wrongful Dismissal?

If you are an HR manager and one of your employees provides you with a letter of resignation, you do not have to provide that employee with reasonable notice or statutory notice. Right?
The answer is that it depends. It depends on whether the employee actually resigned voluntarily and intended to do so. If an employee believes she is about to be dismissed, and decides it is better to quit than be fired, then there is a good chance the employer still has to provide notice of termination. If the employee is being driven out by the employer, then a quit is not voluntary and will be treated by the court as a dismissal without cause entitling the employee to proper notice of termination.
There are lots of cases on this point. The latest is from B.C., called Chan v. Dencan Restaurants, issued earlier this month.   Chan worked for a franchisor of Denny’s restaurants.  Twice he was told by his superior that he should consider quitting because otherwise he would be dismissed.  He actually resigned twice, but then was hired back.  Then, in October 2010, the manager once again told the employee that he should quit, or he would be fired.  The employee decided to resign, and sent a letter saying:

After my vacation ended a week ago, I then realized that my wife needs my attention more than I anticipated as well as looking after my own health–advised by my family physician to slow down.

In fact, none of that was true, but the employee felt he was about to be dismissed and wanted to “save face”.
The Court noted that a resignation letter is not a resignation.  It is only evidence of intention to terminate the employment contract.  The real question is “who terminated the employment relationship?”  The Court observed:

When an employee is left with no choice but to resign or be fired, the resignation is not voluntary and a letter of resignation is tantamount to a dismissal: Deters v Prince Albert Fraser House Inc. (1991), 93 Sask. R. 205, 4 W.A.C. 205 at para. 13.

This is what happened in this case, the Court ruled.  Therefore, Chan was entitled to damages for “reasonable notice”.  Since he was a long service, managerial employee, aged 63, the Court set that notice towards the outer limit of notice, at 18 months.  The Court noted that the repeated threats to dismiss the employee if he did not quit “come very close to meeting the test of unfair or bad faith conduct” in the manner of dismissal (Honda damages).  Very close?  I’d say that behaviour is well within the range of the bad faith dismissal.  However, the Court refuses to order those damages because the employee had not present expert medical evidence that this misconduct caused him additional physical harm.   The employees’ doctor was called as an witness to testify that the employee had been prescribed anti-depressants.  However, the doctor had not been tendered as an “expert” and therefore could not testify as to the cause of the depression.
What should an employer do when it received a resignation letter from an employee under circumstances in which there is reason to doubt that the employee truly wishes to quit?