To avoid tear-outs it's necessary to use brand new router bit, high speed setting on the router, and very very shallow passed. It's also adviceable to check the direction of the grain, as direction of routing can have huge effect on the occurance of tear-outs. In some areas you just can wait for it to happen (routing parallel to grain).
Tear-outs have happened to me in the past. For planned solid color it's no biggy. Bondo type car filler will take care of that.
For stains or natural colors it's wise not to route at all. Chance of tear-outs is simple too big, whatever your technique and precautions. For natural colors and stains bandsaw body close to spec, let Robosander type set-up bring you even closer to final shape, but do final work by hand.
I've had a tear out like this happen once to me - I did 3 flying V body blanks at once and I ran one of them through the router a little too fast If you're going for a natural finish, I say try contouring the horn differently as to minimize the tear out if you don't mind a slightly different shape.
I would try to fix the tear out by cutting a thin piece of mahogany veneer, cut it in the shape of the tearout and glue in place. You'd be surprised at how good the fix might look. you could make the tear out a more regular shape to make the fix easier.
You don't need a new bit for every project. That's just crazy. All you need is to take your time and take small passes, especially when running the router bit cross grain. Most people use tools with little or no experience and end up with problems like this.
When routing, you should always do the cross grain parts first and take it S L O W. The bit bearing doesn't have to touch the template when making the first couple of passes. Firmly grip the piece to be routed and run it by the router bit until the bit bearing touches the template. You shouldn't attempt to touch the template right, unless you're within 1/16" or less from the cut line.
Where did you get the sustain block? Did you make it yourself? I want one!