If I delete an episode from my iPhone, will it still be available on iTunes?
It depends on two things:


If you have a computer or another device set to automatically download purchases, you will have that copy as long as it is online and the download completes successfully.
If your account is in a country that allows TV eposides to be re-downloaded (usually called iTunes in the cloud) you could re-download the episode later as long as the studio doesn't withdraw it from sale or download.