Paycoin is a pointless clone wrapped in a blanket of scam, but there are alt coins that are innovative. Bitcoin will fade for the same reasons that first-generation technologies always fade. The sooner the better.
Bitcoin will fade just like email, the Internet, broadcast radio, internal combustion powered automobiles, railroads, batteries, QWERTY keyboards and cellular telephony. Boy I miss those things...
You're comparing a specific instance of technology (bitcoin) with broad categories (email, etc.).
Cryptocurrencies aren't going away. Neither is email.
But the first networked email wasn't the email you're using now. My first email address looked something like "utzoo!decvax!harpo!eagle!mhtsa!ihnss!ihuxp!grg" (called a "bang path"). The transport was UUCP, over dialup modems.
You're still using email, but you aren't using any of those technologies that got networked email off the ground. In the future you'll still be using cryptocurrency, but you won't be using bitcoin (and probably not anything that currently exists).
EDIT: the way bang paths evolved, with various things done to continue making use of the underlying technology and make it more convenient and add features, reminds me of all the side chain stuff. It's not a bad thing, it's a way of keeping an existing infrastructure useful. But eventually designing something from the ground up wins out over putting bandaids on top of an obsolescent foundation.
You are not considering the inertia associated with network effects. The reason the internet has never upgraded from IPV4 to IPV6 is because too much hardware and software is dependent on IPV4. Bitcoin is like IPV4. It's just a base level protocol on which innovation can be layered.