Does removing an iPhone from my icloud account also erase the data?
The erase command can't be delivered until the device connects to the internet. The same with issuing a passcode lock. 

The device will remain unlocked, unprotected, unearned until such time as it connects to Apple's servers.

That being said, a destroyed phone is unlikely to be unlocked or even work, but there's a chance your data is vulnerable if you cannot assure destruction by locating it and shredding it (or equivalent).