How do we know posterior vitreous detachment has completed, is there any way to know this, I mean in young high myopic like me, will it last forever?

Yes. Your ophthalmologist will be able to know if the PVD is complete, but you may well have symptoms forever.
Not forever but slow. The solid gel vitreous changes to a dense syrup once it starts over about a 25 year period In most cases while there are sometimes symptoms like floaters, and light streaks, the outcome is benign. Rarely there are strong attachments to the retina which can be threatened. If you have continuous symptoms or loss of vision, see an ophthalmologist right away.

Related Questions

If posterior vitreous detachment happen in yung high myopic like me without retinal tear, is der a chance of future retinal tear due 2 cataract/glucoma?

Higher. The risk is probably 10 x greater than a patient without these characteristics. Risk ia about 1/1000 unless you have a family history. Having glaucoma and a cataract do not increase this risk. Having cataract surgery does increase the risk of retinal tears. You should talk your eye md. Read more...
Unlikely. Vitreous detachments can cause retinal tears and rarely vitreous hemorrhage. Retinal tears can cause retinal detachments. Once a vitreous detachment has occurred without causing a retinal tear it is unlikely to lead to additional pathology in the future. It does usually cause floaters which can be annoying. Read more...