Can I change "has" to "is" here?

Isn't it right to say "Love is gone"?

Normally, the order of English sentences are subject + verb + object, but in some cases you use the structure object + subject + verb. This is normally used when there is no context before the sentence for emphasis. However, it sounds very old-fashioned and is not generally common to use. In this case, she most likely uses "gone is love" instead of "love is gone" because it is an older expression, and sounds dramatic when it is used nowadays. This is common with sentences of this structure, as often times they are older expressions, sayings or idiomatic phrases that are used to make a sentence sound more dramatic or elevated. Ex: Long over are the days of our youth. Ex: Clever is the man who saves his money.

What does "work like a charm" mean?

When something "works like a charm," it means that it works very well or effectively. Ex: Wow, this trick works like a charm. Ex: Just try out my advice. I guarantee it works like a charm.

What does "better still" mean here? Is it something like slang?

"Better still" is an expression that is used when you want to include another idea on top of a previous one that you think is better. You can also say "better yet". Ex: Add some lime or better still, some lemon juice. Ex: If you buy a guitar or better yet, an electric guitar, you can plug it into an amp and play it loudly.

What's the main difference between a "clip" and a "video?"

A video can be any length of time and can show a full or shortened version of something, like a full film or one scene from a film. Meanwhile, a clip is always a shortened version of a whole thing. Ex: Show me that funny clip from the show. Ex: Can you rewind the video? I missed part of the scene.

Can I change "has" to "is" here?

No, you couldn't use "is" instead of "has" here! That's because the present perfect tense is used here: "has/have + [past participle]" is the present-perfect form, which means that an action was completed in the past and is still true or relevant now. Using "is" wouldn't fit the tense or the context. Ex: She has eaten already. => already eaten Ex: She is eating already. => still happening Ex: They have won the competition.