I suppose the one nice thing is that this won't take as long as the Nylander situation. Can't have his cap hit inflate due to missed time.
This is actually a misconception. The cap hit the team takes doesn't inflate, it stays the same. It just gets squeezed into a smaller and smaller fraction of the season which implicitly inflates the "full season" cap hit.
See this page here:
Toronto Maple Leafs Daily Cap Tracker - CapFriendly - NHL Salary Caps
The cap hit the team actually took on for Nylander was $6,962,366 over 126 days. The higher $10.3 million amount that everyone talks about is just the annualized value: $6,962,366 * (186/126) = $10,277,778. This number is used because CapFriendly likes to put everything in terms of neat annual amounts (which is why you see cap space appear to increase over the course of the season).
The reason for the rule is not to punish teams by inflating the cap hit it's to stop teams from forcing RFAs to sit out until December to game the system. Basically, the rule is that regardless of when you sign the player, you're going to count their full AAV over the course of the remainder of the season whether there are 186 days remaining or 126 days remaining. If not for this rule, teams would actually get a lower cap hit in Year 1 if they forced RFAs to sit.
So, if the Leafs have $10 million to sign Marner on October 1st next season they'll still have the same $10 million to sign him on December 1st (assuming they don't use it, obviously). His "full season" cap hit will have increased but the cap hit the team actually takes for the remainder of the season will still only be $10 million.