We see that's some of the cryptocurrencies ranking level are decreased such as dogecoin before it was ranked #4 but currently I think it doesn't listed even in top #10 ranking... So can bitcoin also decrease its rank in the future or it will remain #1 rank forever?.
i can certainly answer that Bitcoin will Last forever because this is the Pioneering (though there are some first crypto but not succeed the market)
but in Ranking 1?nope there is no forever i think because there are many crypto currencies that is created Good or more than Bitcoin and just happen that for now harder to find support from the community but in time?sure they will blossom and make another step to serve crypto people in future.