Либо-versions are really bookish. Use нибудь instead for everyday conversations.
"либо" is used there because hmm...it's written by someone who doesn't know that "нибудь" exists.

About the grammar:
The key thing there is the verb "узнает"

Узнает has a subject and an object just like any other verb.
Subject here is supposed to be a human being.
Object is hmm...some information (you chose prepositional case, let it be so).

The ending of узнает HERE corresponds to a nominative singular form.
Thus, use singular/nominative for кто-либо/кто-нибудь.

It was an explanation from the sight of "why узнаЕТ needs кто-нибудь".

If you're trying to compose a sentence using this pattern, here's another one:
I would try to avoid translation from English to Russian.

The main pattern for this sentence is the next one:
Если -> condition -> то/тогда -> positive consequence, иначе/в противном случае -> negative consequence.
Positive/negative are not subjective ones here, but objective ones, that depend on if the condition is accomplished or not.


The "condition" here is a simple declarative phrase in the future tense, like:
сегодня будет солнечная погода (imperfective);
мы поедем налево (perfective), etc.

The positive and negative consequences use the same phrase patterns as the "condition".
Мы пойдем гулять;
Мы заедем в тупик;

Now let's apply the pattern:
Если [сегодня будет солнечная погода], то [мы пойдем гулять], а если нет, то [мы останемся дома].

Now let's rip apart the "кто-нибудь об этом узнает". It obeys the general rules of SIMPLE sentence composition. Learn it.
It's a simple declarative sentence in active voice preferrable pattern is [subject -> verb -> object]. But any variant is good, except thIS phrase should not begin with a verb. Of course, any additions of time, etc, are allowed at any position, but don't break apart word combinations, like if you chose "маленькая девочка" for the subject, don't insert anything in between the words.

The verb/action here is the "узнать". The phrase is "dancing" from it.
The subject here is "some person". It could be any noun/name, and I don't see any reason to use any other case than the nominative one.
And finally, the object is "это".

And, excuse me, I'm too lazy now to write more