Related: Ageism plagues workers

And a survey by the Transamerica Center for Retirement Studies reveals that nearly two-thirds of retirees ended up on the couch instead of the job sooner than they anticipated because they were laid off, their company reorganized and left them without a position, or because they were generally unhappy with a job and just couldn't stand it any longer.

Just 16 percent of retirees who retired earlier than they expected took the exit because they felt they could financially afford it.

"If you plan on working longer as a way to get by in retirement, you are going to be in trouble," Craig Copeland, senior research associate at EBRI, is quoted saying in the report. Copeland adds, "It should be a complement to a solid savings and spending plan, not the foundation."

That's all very well to say, especially when it's a little late to do anything differently, but the point is that there are many factors that can derail a retirement—so anticipating the possibility can help you prepare for the worst and possibly avoid it.

A Denver Post report looks at the situation of a couple in which the husband has been compelled to leave his job due to vision problems that, while making it impossible for him to continue as an ultrasonographer, do not make it impossible for him to work at all—although another job would be at a far lower pay scale.

And while he's applied for disability under a policy he has, it's out of the question for him to apply for Social Security Disability Insurance—so if his claim on the policy is denied, he has no disability recourse. And that's affecting the entire structure of the couple's retirement plan, although—more fortunate than most—they're in a pretty good position to begin with.

Others aren't so lucky. And even if they stay hale and hearty till the very end, employers may not want  them; a Prudential report finds that when an employee delays retiring, it costs the company $50,000.

On a company-wide level, the report finds, delayed retirement can increase overall workforce costs by 1 percent to 1.5 percent—so even if you want to stay on the job, your employer may simply show you the door.

So if one of these, or another, scenarios happens to you, be prepared:

• Cut spending now rather than waiting till you're actually on the way out that proverbial door.

• Save more while you have a chance.

• Maybe move jobs earlier rather than later, since research by the Center for Retirement Research at Boston College indicates that 55 percent of people in their 50s who attended college and voluntarily switched jobs continued to work to age 65, compared to 45 percent of workers who didn't go of their own volition.

• And last but not least, keep your skills current, and network for all you're worth—it will make it more likely that you'll be able to postpone the day you walk out that door for the last time.