In a new interview with Shigeru Miyamoto, he reveals that in the future card versions of Amiibo characters will be available once that figurine has been discontinued:
When asked about any planned “digital versions” of discontinued figures, he stated:
We’re not making promises for certain figures, but the way “amiibo” is designed is that certain games can have “amiibo” specifically for that game. Other games can take advantage of past “amiibo” that developers want to make their game compatible with. In the future, we have the option, if certain “amiibo” figures are no longer available in stores, to release an “amiibo” in card form with the same functionality.
Sounds like good news for those worried they’ll miss out on training up their favorite characters in Super Smash Bros. or on any of the other features Amiibo will provide in current and future titles. However, I’m sure there are some out there who would prefer to actually own figures instead.