Those holes were exploited by Harbor, Jason Avant, and Brent Celek earlier in the season.
Not surprisingly, the offense has dipped, and the team has lost three of the last four games while Jackson missed one game through a team-imposed suspension, and Vick (ribs) and Maclin (hamstring) missed three due to injuries.
The Eagles averaged 25.4 points and 434.4 yards per game through their first eight games of the season, with Vick, Jackson, and Maclin all starting each week.
In the last four, the Eagles have averaged just 17 points per game and put up 369 yards of offense. They have scored 20 points or fewer in each contest.
Their biggest output, 466 yards against the Patriots, was padded by late-game passing after the result was not in doubt.
"To kind of get the backbone back will be pretty cool," said Maclin, who was officially listed as limited in practice but said "it's looking pretty good" for playing Sunday.
Maclin remains the Eagles' leader in receptions and receiving yards.
Offensive coordinator Marty Mornhinweg said he expects his backups to step up whenever a starter gets injured, and by this point in the year every team in the NFL is coping with injuries. But the Eagles' dip shows just how much an offense can be thrown off-balance when missing a few key parts, especially a starting quarterback.
"A lot of teams have been focusing so much on me," running back LeSean McCoy said. "Now we've got the full team back, it's a lot to watch out for."
McCoy has gained a robust 4.8 yards per carry the last four weeks. But he was averaging 5.5 per rush with the full team involved.
Avant has been limited to just one reception in three of the four games without Maclin or Jackson in the lineup. Before, he was getting matched up with linebackers as teams focused on Jackson and Maclin and was a bigger contributor.
The biggest factor could be Vick, who takes over for Vince Young after the backup threw eight interceptions in three starts. Vick, though, had thrown three interceptions and no touchdowns in his last two games before broken ribs sidelined him.
The Eagles' 29 turnovers and 22 interceptions both lead the NFL.
"We're ranked very highly in almost every category. The ones that we're low, and there are important ones where we're low, are directly correlated with turnovers," Mornhinweg said. He pointed to the Eagles' 21st ranking in red-zone offense. "We'd be in the top five if we hadn't turned the ball over eight times, right? . . . The biggest statistic that correlates with winning or losing is turnovers."
Even with their full slate of offensive stars, the Eagles got off to a 3-5 start.
But on a team looking for any help they can get, the return of key cogs in the passing game should help as the Eagles try to remain mathematically alive for at least one more week.
Contact staff writer Jonathan Tamari at 215-854-5214, email@example.com, or @JonathanTamari on Twitter.