What happens if I cancel my account?
Yes, you can play until your current subscription period ends after cancelling - what you're actually cancelling is only the automatic renewal of the subscription.
Your account and characters are very likely to be held for a long time, but there is no guarantee for this in the Terms of Service. However, it's very common in MMORPGs to keep accounts for years if not for the lifetime of a game as the only reason to ever expire them is to free up character names.