bitcoin will be replaced with other cryptocurrency or maybe new highest digital currency "if" no people trust in bitcoin value, no new investor come, and no developer activity
If most of the people will truly remove their trust in bitcoin, no way they will trust other crypto too.
After all years that bitcoin really takes some good and positive progress, adoption, usage and development and still got wrecked you think people will trust other crypto too?
If the other altcoin is developed actively and has good community support, people will support it like the bitcoin.