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.
It really depends on what you're looking at.
Most of the apparent level scaling (i.e., Master Conjurer instead of Novice Conjurer) is simply the game looking at the player's level, comparing it to the Conjurer-Type Enemy List, and pulling out the appropriate mob.
So in that sense, there is a cap on the leveling, since once you level past a certain point, the game will always pull from the highest box (i.e., Master Conjurerers everywhere).
However, this is different for different lists, with Dragons, notably, maxing out at level 78 (when Legendary Dragons begin to appear).
But that said, if you're already approaching level 81, I think it's likely you've hit the cap on most of these, and they will get no stronger.
While I haven't been able to verify for sure, I think there might be a few quest mobs (non-radiant) that have strict level-based scaling, but these would only be a minor fraction of any fights you might get into -- the exception, not the rule.
You should be able to consider the scaling to have stopped around level 50 for most things, though.