>>11235535That's the point. Japanese don't want to end on a consonant, so they insert a really neutral sound there. But it's so neutral so that they can almost omit it. In it's softest form it becomes just part of their accent. I'd say that there is almost no case where "it isn't there", because it always twists the pronunciation slightly.
Due to speech entropy, having a such a repeated phoneme in your language will NOT last. Humans will stop using it, unless it is so neutral and natural that you CAN say it so softly that it is inaudible for non-natives.