Ahriman
Tyrant
since offline mode won't work unless the client is updated at the time you set it to offline mode that would actually be fairly easy to accomplish for most players
Which is why you update the client, pay the fee for say 1 month, go offline, cancel your subscription. So yeah, you'd have to pay ~1 month subscription each time you wanted to reinstall.
Unless cancelling your subscription (a financial transaction) can somehow forcibly uninstall your Steam client or force it to connect or wipe its offline mode, I don't see how they could stop you.
I guess they could eliminate an offline mode entirely. Would be technically feasible.And one shouldn't assume that the client would continue working the same way