My ideal portfolio looks like this when it has 80% of bitcoins. The remaining 20% is probably ethereum and some other altcoin. But at the moment I have only 30% of bitcoin at my portfolio. But I strive for the ideal.
Since you are holding 70% on altcoins and their performance has been so bad then you may as well keep holding them, I doubt that altcoins are going to go down that much lower, so take advantage of this, however this only applies if you are holding valuable altcoins that are in the top 20, if you are holding altcoins that are outside the top 100 then you should consider the possibility of selling for a loss before it gets too late and you lose any chance to get some money.
But once we see the market of altcoins recovering you could sell your good altcoins in exchange of bitcoin and get to your desired portfolio.