I disabled my network adapter and then launched the game. It simply didn't retrieve my online characters, but I could still play my offline characters just fine.
Whoever put on this wiki that all modes require an online connect to play is incorrect.
I even launched the game directly from the d2r.exe and did NOT have battle.net open. It works just fine, even when I want to play online with bnet not launched.
battle.net is probably required for stuff like friends list or chat maybe, I don't know exactly. But I can play the character online without bnet launcher running.
I don't know how to update the page to properly reflect this, but one of you Chads needs to reconfigure it so that it reflects that offline play is available.