What are the basic options?
Sketch endings
1. The funniest joke in the world
2. An amazing twist you didn't see
3. A telegraphed twist
4. A lame joke
Fade out.
Nogget, how long you've been writing?
Quote: Will Cam @ 4th October 2017, 11:02 AM1. The funniest joke in the world
2. An amazing twist you didn't see
3. A telegraphed twist
4. A lame joke
Or, if you're a Python, a uniformed officer coming on and saying the sketch is silly, and must be stopped.
In other words, they couldn't write endings.
Quote: Paul Wimsett @ 5th October 2017, 3:39 PMNogget, how long you've been writing?
I think the question is, how long have you been writing?
Just thought you'd know.
I mean, the question is, literally, "how long have you been writing?", not as you wrote, "how long you've been writing?".
"How long you have been writing?" is more interrogative but still correct.
reversal " hence george pulling out a tidal golf ball" human brains are repetitive by nature. An ending to a scene at the start that the audience is thinking, then it gets figured out.
I would say figure out more of the word best ending. Figured that out is the number 1 though. A completed scene at ending. Humans arn't stupid , you have the subconcious to deal with along with memory an uncompleted joke or scene finalised
thats the word finalization.
Quote: Paul Wimsett @ 5th October 2017, 6:09 PM"How long you have been writing?" is more interrogative but still correct.
Not in any native English dialect that I'm aware of. (Or am I missing the joke?)
Sounds like something Bertie Wooster would say to me, which is probably a good guide for "spoken English", if not written.
"Tell me how long you've been writing" and "Tell me, how long have you been writing?" Are both correct but have different meanings, the first a straightforward request and the second with incredulity.
I think , without sounding facetious, your options are to have an ending, or to have no ending.
If you decide to have an ending, there are many different ways to do it. Ideally, as stated above, use the funniest joke in the world, but I find that a lame gag, or even a non-joke that creates closure, will work as well, it just nicely cauterises the preceding comedy operation.
For example, I wanted to write a sketch about people asking for sponsorship to do something they clearly really want to do, or were going to do anyway, because it annoys me, so I wrote a sketch about a salmon asking another fish to sponsor it to travel across the world to spawn. I thought this was really funny, but couldn't find an ending. My friend stuck in "Who are you collecting for, anyway?", "The local school". Now, educational school/school of fish is a dire pun, but it just capped off the sketch well. So, in short, if you want an ending, a clear ending is best, even if it's not as funny as the rest of the sketch. Just my opinion.
Obviously, not having an ending can go two ways: make something of it, by going meta - Python technique as mentioned - or just walk away. Funnily enough, if you watch really old sketches, or sketches in the literal sense of drawing a character or scenario briefly, they often end with nothing much: "So long, then, Nobby".
There's a third way, which I confess I use far too often, which is the sudden tonal shift, implying a conclusion when really there is none at all. So, you could have two nuns discussing the latest wimple fashions, with lots of nice little gags, and then end with, "Also, I'm quite partial to the new, mother of pearl rosaries", "Oh f**k off, they're shit". It's actually a bit depressing how well this works. The acceptable family version is sudden disappointment putting a cap on the discussion: ""Also, I'm quite partial to the new, mother of pearl rosaries", "[SAD] You've gone too far, Mary, far too far. [BEAT] I'll pray for you".
If all else fails, blow up the room. 
Quote: gappy @ 9th October 2017, 10:53 AMIf all else fails, blow up the room.
Violence as an ending is interesting, since the shock seems to act as a definite 'full stop'.
There is a Mitchell & Webb sketch in which Robert Webb is an interviewer who is only there to give 'extreme negative feedback', and at one point starts using a typewriter, not for any particularly relevant reason; but it prefigures the end of the sketch, which involves him throwing the typewriter at the interviewee's head.
Not a clever ending at all, but it gets a laugh.