There's literally no way to quantify that without extrapolating from sample sizes that are too small to responsibly produce intelligent hypotheses.
Agreed, Marner only played parts of a dozen or so games in the middle this year and sometimes Hunter didn't even make it full games as when behind on the scoresheet, it wasn't uncommon for him to reunite his big line as he shortened the bench in games to generate more offense.
The reason the sample sizes are small is because the plan of Dvorak centering 1 line and Marner another didn't pan out as expected. Why did it fail? Having balanced scoring as opposed to all ones eggs in the same basket should have benefited the Knights attack not hindered it, resulting in the plan to be scrapped. The trio of Tkachuk -- Dvorak -- Marner is so deadly offensively that even a 1 line attack must have outweighed the advantage of spreading out the scoring.
However (
IF) Marner should be returned to junior next year and with Dvorak graduating to pro there really would be no reason why we wouldn't likely see a Tkachuk -- Marner -- Jones top line.
The one silver lining of a Marner returned to junior would be development as a centre, which would be a different situation to challenge Marner to now carry the Knights (without support from co captain Dvorak). If Marner is too good as a RW in junior with nothing left to learn or prove, them playing centre and new position for him would increase responsibilities in the FO dot and defensive zone coverage etc etc.
If management don't keep Marner with the Leafs next year then this might be one thing on the table that they're considering as a benefit of a return to junior for another year to get stronger as well as mastering another position and doing it without a linemate (Dvorak) which has been a dynamic offensive duo in junior the past 2 seasons.