Ok, I'll be in opposition of most replies, AND as a taxidermist, I'll give my rationale. If the split is very small, under an 1", I usually will leave it as is. But as the split gets deeper, I am in favor of repair for the longevity of the mount. Let me explain, if the taxidermist is doing a bondo ear, there is a decent chance over time, the cartilage left in the ear with begin to shrink, causing stress on the structural integrity of the ear to remain in the mounted position. The smaller side of the split could begin to curl, usually inward, as it is cut off from the strength of the other part of the ear to hold it in place.
Depending on the shape of the split in the ear, an ear liner might not be feasible to make work.
Any bumping/dropping on the ear over time through moving etc, could also result in greater damage (see structural issues above) than if the ear had been repaired.
At the end of the day, the customer decides, but I do favor the repair. IMO