Once the desired size is met, you can leave the taper in or move to a tunnel that simply just keeps the ear stretched but doesn't stretch it any further.
Once this is left in for long enough, usually worn as jewerally / fashion statement, the ear won't return to it's original size. It may shrink a little if taken out for a long period of time but this is because the tissues aren't needed in their larger size.
If this size increase was the penis, atrophy (shrinkage / loss of size) would only happen if you didn't use your penis. Simply retaining your new size can be as easy as... masturbating or having sex regularly.
If you happen to fall back a little from lack of use and lose a little size, you know the formula to gain the size again.
The second time around or any time after is usually a lot easier, if you need to regain that tiny percentage of size loss.
Again, to lose that size you would literally have to not use your penis for a long time.
And like most things, what you don't use...you lose.