When a land is turned into a creature by some means, unless it specifies that it's "Still a land" (Celestial Colonade) then it's not considered a land anymore, which is important for spells that depend on land count (
Boundless Realms).
When it dies, the card reverts back to being a land, so
Extirpate couldn't find it.
If you're looking for a good card to go with your theme, and you're in modern, check out
Eradicate. it's searching for "cards with the same name" so it's not restrained by the creature/non-creature distinction. The same combo can be found in green with
Liquimetal coating +
Splinter