It is less than 0.1% .Relax ,not all high myopes have retinal detachment.  On the other hand even moderate myopes  carry a risk of retinal detachment. A high myope should have regular yearly retinal check up, or as advised by the ophthalmologist. This will help diagnose and treat peripheral lesions in retina in time. These peripheral lesions are the cause of retinal detachment in high myopes.

Yes there is a possibility that Retinal detachment might never happen in a myope. But risk is always there. So it's mandatory to get your retina checked by a Retina specialist atleast once a year.