Tyler Bozak, James van Riemsdyk and Phil Kessel were one of the more lethal forward lines on offence in the NHL over the past three seasons. But now that Kessel is off to Pittsburgh, the most intriguing question heading into 2015-16 for the Leafs is how his absence will impact his former linemates.

In a recent article on Sportsnet.ca, Bozak was posited as one NHL skater likely to regress this season. This seems obvious, but the degree to which Bozak relied on Kessel for offence is difficult to over-state.

When Bozak was first signed by the Leafs, he spent half a season in the AHL, posting four goals and 20 points with a 6.2 shooting percentage in an underwhelming 32 games.

When he was called up to the Leafs full-time in mid-January of that season, he found himself centering Nikolai Kulemin and Kessel. The line stuck together for 30 games until Kulemin sustained a season-ending hand injury. In that time, Bozak produced 23 points (0.77 pts/gp), Kulemin posted 21 (0.70 pts/gp) and Kessel registered 31 (1.03 pts/gp), a pace that presaged his peak efforts in subsequent seasons.

Interestingly, in 325:52 of 5v5 ice time, that line maintained 50.7 percent of the shot attempts and 55.6 percent of the goals in 2009-10. It could be argued that Bozak’s rookie season represented the peak for him and Kessel, who would never see possession numbers like that again.

The reason why should be attributed to the inability of Leafs management to balance the lineup in subsequent seasons. In 2010-11, Kulemin was returned to Mikhail Grabovski‘s wing opposite Clarke MacArthur in what became one of the best second lines in the NHL. Joffrey Lupul was put on Bozak and Kessel’s line, but his offensive skills never adequately compensated for his defensive deficiencies and injury woes.

With the MacArthur-Grabovski-Kulemin line sheltering them from tougher minutes, the Lupul-Bozak-Kessel trio became offensively productive, if defensively unreliable. They played 1,019 minutes together across a season and a half and managed to register 48.5 percent of the shot attempts while they were on the ice and 49.8 percent of the goals. Lupul saw his production jump to 85 points in 94 games (0.90 pts/gp), Kessel had 146 points in 164 games (0.90 pts/gp) yet Bozak only managed to produce 79 points in 135 games (0.59 pts/gp).

In 2012, when the Leafs acquired James van Riemsdyk from Philadelphia for Luke Schenn, van Riemsdyk had yet to develop into the top-line talent the Flyers thought they were getting when they picked him second overall in 2007. The Leafs were hell-bent on ensuring JVR would get every opportunity to develop as a first-line producer.

After his arrival, the Kessel-Bozak-van Riemsdyk line played more ice time together than any trio in the NHL—more than 2,300 minutes together at 5v5 and on the power play across two and a half seasons. Just to illustrate how mind boggling that is, no other line combination has played more than 1,600 total minutes together since the 2007-08 season. Toronto’s top unit played all these minutes despite failing endlessly on defence.

Since JVR’s arrival, at least two members of the line were directly involved in 48 power-play goals and 110 even-strength markers—26.7 percent of Toronto’s 591 regular season and playoff goals during that time. However, the line also allowed 150 goals against at 5v5 when at least two of them were on together, which is abysmal compared to other top lines around the NHL.

The offence was always the saving grace for this unit, but the unfortunate reality for Bozak and van Riemsdyk is that, to all appearances, they have a tough time producing without Kessel.

Across Bozak’s entire career, 85.5 percent of his 5v5 and PP ice time has come alongside Kessel, 65.5 percent of his points have come on goals directly involving Kessel, and more than 90 percent of his points have been produced with Kessel on the ice.

In his 878:08 of 5v5 ice time away from Kessel in his career, Bozak has only managed to produce three goals and 11 assists. That translates to a 0.96 points per hour rate, which is smack in the middle of fourth-liner territory. Because of Bozak’s inability to drive offence on his own, and the focus/fixation on bottom-six checking line centres having a strong faceoff ability, it seems quite plausible that Bozak will have to shift to a more defensive role this year.

A quick glance at the list of NHL centres with comparable offensive production at 5v5 over the past three seasons should make that clear:

Similarly, we haven’t seen much of van Riemsdyk without Kessel, but what we have seen isn’t encouraging.

The two wingers spent 2444:21 together at 5v5 and van Riemsdyk produced 33 goals and 78 points for 1.91 points per hour, which is basically upper second line material. Away from Kessel, he managed a far less flattering 10 goals and 16 points in 671:42 of 5v5 ice time, which translates to a mediocre 1.43 points per hour.

That type of scoring rate is typical of third line talent in the NHL.

Van Riemsdyk has actually scored on fewer of his shots than one would expect based on their location and danger level. But he hasn’t shown much of an ability to create more offense for his linemates and his poor defensive showings at 5v5 over the past few years were a significant factor in what dragged the Leafs’ top line down.

But because he’s the reigning goal leader on the team, still only 26 years old, and has a good scoring-chance rate, all signs points to van Riemsdyk remaining in Toronto’s top six. What is still unclear is if he can mesh with Nazem Kadri, who is very likely to see a significant increase in offensive opportunities this season.

In 510:45 of 5v5 ice time with Kadri as his centre over the past three seasons, van Riemsdyk produced just four goals and 12 points—a 1.41 points-per-hour rate. That isn’t going to cut it as a top line winger.

For comparison, Daniel Winnik, Mike Santorelli and Richard Panik all had better production rates alongside Kadri. When you consider that Lupul also has a solid history with Kadri, it becomes less certain that van Riemsdyk is a good bet to play with the Leafs’ presumptive top-line centre this season.

Kessel’s departure was bound to cause a tectonic shift in the structure of the Leafs lineup, but the degree to which it impacts the remaining roster players from last season will likely surprise many observers.

The make-up of the top six will be a discussion point as the team heads into its rebuild and sorts out where skilled players such as Mitch Marner and William Nylander fit into the mix. Unfortunately for incumbents Bozak and van Riemsdyk, if their production without Kessel drops as significantly as it looks like it could, their future standing on the roster will be in question.