Formal:
* If so: This works when "if ever" is used to refer to a previous statement.
* Should it ever: This emphasizes the possibility of something happening in the future.
Informal:
* Ever: This is the most common and casual shortening.
* If/When: This works if you are implying a conditional action or time.
Example:
Original: "I'll be there, if ever."
Shortened: "I'll be there, ever." (informal)
Shortened: "I'll be there, should it ever happen." (formal)
Ultimately, the best way to shorten "if ever" depends on the specific context and your desired tone.