I saw this today in a Vonage commercial.

Problem:
The adverb does not match the tense of the verb.

Explanation:
The adverb “yet” means at the present time.

The expression “didn’t leave” is in the past tense, so “yet” does not go with “didn’t leave” (or any other expression in the past tense).

In other words, it makes no sense to say, “Hope you didn’t leave at the present time.”

To fix this, one must change the expression to the present tense.

Solution:
“Hope you have not left yet.”