I am nearing level 81 (the max level without legendary skills), and want to know whether I after that no longer have to worry about level scaling or what. If level scaling doesn’t stop then does it slow down or stop at some other point?
Different things in Skyrim scale differently.
Creatures and un-named NPCs generally always pull from Leveled Lists, and have fixed stats and levels. So, for weaker animals like Wolves, the strongest version are level 6, beyond which they stop scaling altogether. For Dragons, however, depending on the DLC you have, there are options up to a player of level 78.
Named NPCs work differently, however. Because they aren’t spawned into the game when needed, they can’t pull from a leveled list. Instead, their level is scaled to yours, within a range. Each NPC scales differently, too. So Jarl Balgruuf, for example, will always have 1.5 levels for every level the player has, except that he cannot go below level 10, nor above level 30. Thus, he stops scaling once the player hits level 20.
Some NPCs don’t even have a maximum level. J’Zargo, for example, will always be the same level as the Player, with a minimum of level 6. The Followers page can be useful for finding NPCs with no, or high level cap.
As a named NPC gains levels, their Health, Magicka, and/or Stamina will increase by a fixed amount per level, and their skills also increase according to their class. So, at a certain point, a given named NPC will max out their various skills, meaning that they are getting less benefit per level.