There is no standard, anyway. What works on one mixer has about a 50% chance of not working on another. For example- my old Alesis Studio 32 was tip-send, and the Soundcraft Ghost I replaced it with is ring-send. So I got to rework my patchbay to swap all the insert pairs. Par for the course: solder is cheap.
This is why the insert Y-cables from ProCo, Gepco and the like are simply labeled "tip" and "ring" on the TS ends. You get to figure out which is which for your hardware!
If Dragon will ever rebuild the search index, you'll be able to find an article I did on "insert stealing"- using the insert as a direct out, either by inserting a TS cable only until the first click (_not_ all the way, which would break the normal and give you silence), or by making a special insert-stealing cable with a TRS connector on the mixer end that has its tip and ring shorted together. But I'm not going to retype it now...
Suffice it to say that when there's no plug in the insert, the jack itself has contacts that short the tip signal to the ring signal and "normal" the signal flow through. By using a TRS plug with tip shorted to ring, you can make the insert jack think there's nothing plugged in- and you still have the signal to use for other purposes.
But I'm not going to retype it, because I really want him to rebuild the index. No smiley.