State securities regulators are working on a rule that could push more advisors to face their mortality by planning how their businesses will continue if they die.

Investment advisors often put off so-called "succession planning," the regulators say. But the problem could balloon as a growing number of advisors approach retirement age, they say.

"Many of them literally keep going until they die," without leaving a firm plan for taking care of clients after they aren't around, said Patricia Struck, who heads the investment advisor committee of the North American Securities Administrators Association (NASAA).

The group, whose members include U.S. state securities regulators, has created a proposed model rule that would require state-registered advisors to develop a business plan in the event of their death or disability.

More than half of registered investment advisors are within 15 years of expected retirement, according to a 2013 study by Cerulli Associates, a research firm in Boston.

Advisors who die or become ill without a plan can leave clients in the lurch. For example, clients may not know their next move in a time-sensitive investment strategy or have to chase after refunds for advisory fees they paid in advance. The situation comes up often, said Struck, who also heads the securities division at Wisconsin's Department of Financial Institutions.

Advisors who fail to plan for those issues could open themselves up to more scrutiny from regulators, who often look for such plans when examining firms, say compliance professionals.

An advisor's duty to act in clients' best interests has long obliged investment advisors to plan for the possibility of their untimely death or protracted illness. But that obligation is not typically spelled out in black-and-white. Instead, it has evolved over time through regulatory guidance and interpretations of advisors' responsibilities.

The U.S. Securities and Exchange Commission, for example, effectively mandates succession planning but through a broader "catch-all" rule that mandates having a compliance program, among other things. The Financial Industry Regulatory Authority, which regulates brokerages, requires firms to have continuity plans so they can assist customers during an "emergency or significant business disruption."

NASAA's proposed rule would require that advisors make succession plans. The proposal also requires separate continuity planning for advisory businesses to run amid emergencies such as natural disasters. The group unveiled the proposal in August and is collecting suggestions from the public until Oct. 1. The rule, if adopted, would be paired with guidance for advisors on how to develop their plans.

A requirement by states would still be a long time away. NASAA members will vote on a plan by spring of 2015, said Struck. Even if it passes, it would still be a model rule that lawmakers in individual states could decide whether to adopt.

State regulators oversee small and mid-sized advisors managing up to $100 million in assets. Many are solo firms or advisors with small staff. Clients at such firms can still usually access their funds if their advisor dies, because they are typically held at outside brokerages.

Nicholas Olesen, an advisor in King of Prussia, Pennsylvania, isn't waiting for directions from regulators.

Olesen, 30, and two other solo advisors have signed agreements with each other to run each others' practices if needed. The three share similar philosophies about business and investing, Olesen said, and he doesn't want his clients left to flounder if he dies suddenly or becomes unable to continue his work.

"I put a lot of blood sweat and tears into this," Olesen said. "I don’t want it just going away."