If you think that Snape didn't have a decent end think about Sirius Black and not to mention Fred Weasley. Snape didn't die without doing his best to make sure Harry was always kept safe. Even when Snape was dying from his wounds he releases a cloud of memories and tells Harry to take them. These in turn lets Harry know about Snape's true loyalties. he may have dies a gruesome death but it wasn't in vain.