Fremantle's plan for Jackson this season to spend significant chunks of games as a big-bodied midfielder were thrown out the window when Darcy was cut down by a concussion and calf injury.
It's proven to be a blessing in disguise, with Jackson hitting career-best form as Fremantle's No.1 ruckman.
The 24-year-old is averaging 19.6 disposals, 5.1 clearances, 25.3 hitouts and 5.4 tackles per match to go with 15 goals, putting him in the frame for the Brownlow medal.
Jackson's dominance in the ruck, at ground level and in attack has played a crucial role in Fremantle's club-record 13-match winning streak.
Former Collingwood big man Mason Cox has been Jackson's chop-out option over the past nine games while Darcy recovered from injury.
But in a big selection call, Cox has been axed in favour of Darcy for Sunday's clash with Gold Coast at Optus Stadium.
Fremantle will go two games clear on top of the ladder with a win over Gold Coast, but Longmuir isn't interested in resting players.
Instead, Longmuir will explore the option of managing certain players during games as the season wears on - with Jackson's bash-and-crash ruck role at the top of the list.
"I think it's something we've definitely got to look at," Longmuir said.
"This week's different. We're off a 10-day break, Everyone's raring to go.
"But it's definitely an option. We know what Sean's best in the ruck is like - it's up there with the best in the comp, so it does give us that flexibility."
Remarkably, Fremantle have only one player on their injury list.
It would have been zero, but Sam Sturt's planned WAFL return this week was scuppered when he aggravated a previous quad issue.
The Dockers lost to Gold Coast by one point in last year's elimination final in Perth.
Longmuir says that heartbreak - and a series of other losses in recent years - played a big part in the team's journey to become a premiership favourite.
"We haven't shied away from what went wrong in those moments," Longmuir said.
"We've owned them, and we've learned from them, and we're using those things to help us become a better side.
"The final was definitely one of those. We've spoken about it a lot. We conceded 45 points in the second quarter, and we conceded 80 for the game.
"We just fell away with our consistency, and we've used that over pre-season to be a more consistent side, be better at handling momentum."
