Companies can capitalize on a fast-changing job market because “Goodbye” may not be forever.

An employee’s two-week notice may seem like the greatest act of disloyalty, but there can be a variety of reasons for leaving a company. Yes, there are some chasing after more money, but for others, the marketplace offers new challenges, a chance for travel and even relocation. Others are retiring after a long career in the industry, and some leave for family reasons.

But goodbye doesn’t need to be forever, and investing in these departing employees can reap rewards down the line. People are one of a company’s few assets that grow in value over time — yet they are allowed to walk out the door.

The Internet links people across the globe, and a company can take advantage of this resource to keep in touch with former employees and track their career growth over time. After all, a mother who leaves to start a family may be open to working flex hours; a retiree may be willing to mentor a new hire or take on a short-term project; and someone active in the industry may soon discover that life is not always greener on the other side.

Professional online networking communities offer companies a way to keep connected with former employees and reach out to passive job seekers. Online employee networks serve several functions. Not only is it a way for former employees to stay connected with current employees and former associates in a password-protected environment, it can also serve as a strategic recruiting tool for mining experienced talent.

With an online employee network, former employees can share what they’re doing, post their resumes online, indicate interest and search for job opportunities. Former employees can search for short- and long-term job assignments and use the network as a referral tool for new hires. A former employee is in a great position to find a well-suited hire since they understand the culture and priorities of their former company.

Companies can use online employee networks to keep in touch with former employees through a strong communications strategy, which promotes the company and its opportunities around the globe. A successful online network can work with clients to ensure regular communications, keep individuals connected, and drive home the message that although they may have left the company, the door remains open.

Online networks also give companies the ability to track a former employee’s career growth and changing aspirations and priorities over time. An employer can use the online network to data mine experienced talent by searching key criteria like technical discipline, years of experience, and mobility preferences. Unlike general data-mining on Monster.com, Linked In and other online networks, that are populated mostly by entry-level talent, corporate alumni communities target experienced talent — an essential advantage in an industry facing an upcoming workforce shortage.

With an industry operating at full tilt, losing experienced employees can hit a company hard. With online employee networks, employers can fill their talent needs by bringing in former employees for short-term consulting opportunities and as mentors to train new hires. Leading industry HR personnel relate that industry experience and knowledge stay valid for up to 10 years. A retiree or a former employee returning from family leave not only helps take the burden off of current full-time employees, but is an ideal way to ramp up new talent.

The days of a life-long career with one company are over. This has been the case for the past 10 years, and it seems this pattern will continue. An employee may come and go several times — as an employee, a short-term consultant, mentor, and recruiter. Companies are working hard to maintain positive and flexible working relationships with employees, and online employee networks help to keep that revolving door turning.

Cathy Clonts is president of Alumni Web Services, a provider of online networking communities and management services to the oil and gas industry. www.AWSinternational.com