"I'm coming back to prove I'm the best—I'm coming back to help my team win a championship," he told Ed Werder of ESPN.
In an interview with Rich Eisen (via the NFL on Twitter) on Dec. 21, Thomas said he was still contemplating retirement:
It's difficult to understate how much his departure would've hurt the Seahawks.
Since their Super Bowl win in 2013, the harsh reality of the salary cap has forced them to let various veterans go over the years. Those personnel departures have impacted Seattle to varying degrees.
The secondary hardly missed a beat after losing Byron Maxwell and Brandon Browner. Golden Tate, Bruce Irvin and Russell Okung, on the other hand, have been harder to replace.
Thomas would've been arguably the biggest loss the Seahawks had suffered. He's still one of the league's best safeties, and had he not gotten injured, he almost certainly would've reached his sixth straight Pro Bowl in 2016.
When Marshawn Lynch retired, Seattle had a clear succession plan. Thomas Rawls had a breakout 2015 campaign, and the Seahawks might have planned for him to be the feature back in 2016—with or without Lynch. Lynch's retirement merely cemented Rawls as the team's starting running back.
The Seahawks' future at safety would have been far less assured without Thomas.
Steven Terrell took over at free safety to end the 2016 season. The 26-year-old played about as well as could have been expected, but there was a clear drop-off between him and Thomas.
Terrell explained how it was nearly impossible for him to make a similar impact to that of his predecessor, per the Seattle Times' Jayson Jenks: "[Thomas] just has that instinctive feel. He can take chances that I can't because [of] his knowledge of the game. He's been doing it more. I'm not there yet, but I'm getting there. I feel like every game I'm getting a little bit better."
Finding a long-term replacement for Thomas wouldn't have been easy.
Eric Berry would have been the only potentially available safety on Thomas' level in free agency, but he re-signed with the Kansas City Chiefs on a massive deal. That would have left the NFL draft, and inserting a rookie into the secondary is always risky for a team with title hopes in the short term.
Thomas' flirtation with retirement may indicate he sees an end to his playing career sooner rather than later. He's signed for the next two years and set to make $17 million in base salary, per Over the Cap. Once his deal expires in 2019, he may choose to walk away from the NFL.
More players are choosing to retire at or near their respective peaks, with Lynch, Calvin Johnson and Patrick Willis the most notable examples.
It wouldn't be a surprise if Thomas is once again weighing all of his options a year or two from now.