A file photo of Thomas Boggs Jr., founder of the legal and lobbying firm Patton Boggs, at the firm’s offices in Washington. (Jeffrey MacMillan/The Washington Post)

The sudden death last week of Thomas H. Boggs Jr., the trailblazing Washington figure who helped shape modern-day lobbying, adds new uncertainty to the fate of the eponymous powerhouse he created.

Patton Boggs recently merged with the Cleveland-based legal giant Squire Sanders following an erosion of its business.

The firm had long been the nation’s top lobby shop by revenue; in 2013, Patton earned $38.9 million in lobbying revenue, more than any other firm. But in the second quarter of this year, for the first time since 2002, its billings were eclipsed by rival Akin Gump, which had hired away several of Patton Boggs’s senior lobbyists, bringing with them about $1 million in lobbying fees for the period.

The shift was part of a wave of departures that resulted in losses in key clients and business over the past 18 months.

At the same time, the lobbying industry at large has moved away from the personality-driven business it once was, as public affairs work and grass-roots campaigning have gained importance as a way to influence a fractured Congress.

Boggs had hoped to stabilize the business as part of the newly named Squire Patton Boggs, before succumbing to an apparent heart attack. His title at the combined firm was chairman emeritus, but he remained influential with clients and was key in preserving the firm’s marquee brand in lobbying.

Many current and former partners credit Boggs and the personal loyalty and friendships he cultivated for holding the firm together long enough for the Squire deal to reach completion, even after litigation involving Chevron nearly thwarted the agreement.

“Tom Boggs is not someone you can replace,” said Kevin Bell, a former partner at Patton Boggs now at the law firm Porzio Bromberg & Newman. “He was an innovator when it came to taking law firms and getting them involved in public policy. . . . It’s hard to replace someone who’s been doing that for as long and successfully as he did it.”

Boggs and his partner, James Patton Jr., began building the foundation of Patton Boggs in the 1960s.

At the time, small boutique lobby firms were the industry standard, and most were led by former heads of federal agencies who became lobbyists after leaving the government. Boggs and Patton envisioned a new kind of lobbying operation — one that was integrated into a major law firm, staffed with lawyers well-versed in the areas of law that lobbyists were looking to change. Today, that model dominates the lobbying industry: Six of the top 10 firms by revenue are lobbying groups housed within corporate law firms. Boggs is credited for pioneering that change, and his firm has long benefited from the brand recognition that comes with having his name on the door.

The industry, though, began to move away from that one-man approach to lobbying, and Patton Boggs tried to adapt.

In 2010, Patton Boggs acquired Breaux Lott-Leadership Group, the lobby shop run by former U.S. senators John Breaux and Trent Lott. The move boosted the firm’s lobbying revenue by about $12 million. But after becoming part of Patton, they continued to operate somewhat separately from the rest of the firm’s lobbying group.

It was not until June, following the Squire deal, that the firm publicly indicated it was transitioning leadership duties in the lobbying group to Breaux and Lott. That plan will continue unchanged, leaders at Squire Patton Boggs said.

“Tom was a guiding light, but in terms of the real nuts and bolts of the practice, over the years, Tom has really caused that to be picked up by other people,” said Jim Maiwurm, chairman of Squire Patton Boggs. “The structure is there already, so the succession has already been carried out. You’re not going to see any change in direction in the policy practice. It’s going to be lively and a leader in its field on an ongoing basis. Nothing is going to change.”

The next few months could be critical for the future of the firm, as partners usually decide by the end of the year whether they plan to leave for other firms.

Breaux and Lott are rainmakers with an established brand and a solid reputation for being the rare former members of Congress who have turned their tenure in government into big business on K Street. It remains to be seen whether it will be enough to replace the business the firm has lost over the past 18 months, when top lobbyists in health care, telecommunications, antitrust and other policy areas took their clients to other firms.

Some former Patton lawyers say Squire has lost the most valuable part of Patton Boggs — Boggs himself.

“I think it will have an impact on the policy practice,” said one former Patton Boggs lawyer who spoke on the condition of anonymity so as not to hurt feelings in the wake of Boggs’s sudden passing. “What Squire ends up getting out of this deal without Tom at the helm of Patton Boggs is probably a lot less.”