Instead and If not

Instead adverb - In place of, or as an alternative to.

If not and instead are semantically related. In some cases you can use "If not" instead an adverb "Instead".

If not adverb - Perhaps; indicating possibility of being more remarkable (greater or better or sooner) than.

Instead and if not are semantically related. Sometimes you can use "Instead" instead an adverb phrase "If not".