Although movement in 5e is not governed by squares, they are probably a helpful model to this particular exercise. Everything in the universe is effectively measured in 5' increments and using squares to model this will give us an effective answer to this question Let's posit a 50' wall
x
x
x
x
x
x
x
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x
x
Now let's look at the veritcal space next to the wall
yx
yx
yx
yx
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yx
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yx
Finally we need to have the flat part on top of the wall, and the space above that
yyyyyyyyy
yxxxxxxxxx
yx
yx
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yx
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yx
Now, supposing our hero starts at the first y (marked a below), and runs up, he runs out of movement at the 10th y (marked b below).
yyyyyyyyy
bxxxxxxxxx
yx
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yx
ax
If you start at a, you might be able to climb up onto the top of the wall. However, if you have a 45 foot wall you are safe. If you have to move to a, a dash would be required to not fall (as you don't have the ability to stay vertical).
The problem here is that if the wall extends at all into the square above the one marked b, then you're in trouble, you have to move into the square above it as diagonal movement is not possible.
This will be both at the discretion of the map makers (if the building extends a bit above the square you're probably not going to move diagonally) and also your DM (he may allow a bit of wiggle room here). Consult your DM before you attempt any 50' wall climbs.
45' wall climbs (and lower) are safe though.
Your question sort of answers itself when you look a this part of the spell
worn or carried by another creature
The language of the first paragraph denotes what you can cast it on at the time of casting, once the ritual is finished it doesn't care as long as it's not dispelled or destroyed. It's just not designed to be cast on other people's items while their in their possession. This does allow you to say, take an item while someone is sleeping, enchant it, then put it back.
The only other spell I could find that should affect attended objects expressly does not, so it seems like the designers don't want you to affect attended items.
From Shatter
A nonmagical object that isn’t being worn or carried also takes the damage if it’s in the spell's area.
Best Answer
As a general rule, the magical item continues to function, however, what happens to the wearer of the shoes is a different matter. Since there is no guidance on what happens to an unconscious creature who is standing on the wall, we will need to make some assumptions. And just because the shoes allow him to walk on walls and ceilings doesn't mean that our assumptions about gravity in the game world stop applying.
If he falls unconscious and is unable to control his body, then it stands to reason he will fall down. The magic item continues operating, but that doesn't mean he is magically stuck to the ceiling (or does it? see below...). I would rule the same for a spider on a wall or ceiling. With no mental faculties with which to maintain control of your body, you go limp and fall.
To be clear, this answer is based on my discretion as a DM, as there is no rule for what should happen here. If I were the DM in your scenario, the character would fall off the wall and down the well (though perhaps not drown -- that takes quite a bit of time in terms of rounds -- usually more than enough to mount a rescue attempt, anyway).
It would also be perfectly acceptable for you, as DM, to determine that Slippers of Spider Climbing do work as sticky pads which always work and never slip off the feet of the wearer, even when the wearer is unconscious and dangling upside-down from the ceiling over a pit of lava or what-have-you.