Could go as high as 80 percent, and if the bitcoin dominance really does reach 80 percent, then the price of altcoin could rise many times if many bull markets come to pass.
Bitcoin will remain dominant and will never see it behind due to its up going graph or improvement it will not come to second or third position and if you look at other crypto coins those have not enough potential and strength to compete with Bitcoin. Furthermore crypto coins other than Bitcoin will take a several years to reach at even the lowest value of Bitcoin.
That will happen if the bitcoin bull run would be of the same magnitude as that of december 2018. As it stands, alts will also recover and would likely bring back old hands to it. The market movement recently proved to be a little more costly for alts than btc