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?.
"Will Bitcoin last forever?" is totally different from "will remain #1 rank forever?"
Will Bitcoin last forever? Of course, not. It will not even last 500 years for sure, not even 200 years. Forever, my friend, is much much more than a million years.
Will Bitcoin remain #1 rank forever? If that means for as long as crypto is alive, yes. Bitcoin will remain to be the number 1 rank until crypto dies.