Aside from checking your account once a month the rograms function offline and even if you cannot go online for a longer period you have 90 days grace period to verify your credentials. Plenty of time to work disconnected from the net.
The last "buy once" version is CS6, which is no longer being updated... Cloud programs ARE receiving updates
CS6 is "buy once and never pay again" software... Cloud is a lower up front cost by monthly subscription