Cannot play offline when login server or API server is down

I only play offline and never connect to minecraft network servers. Today, I tried to open the game and saw the messages:

1. The login server is down.
2. API Server down. Changing skins will not work.

The normal logon button has changed to one saying: PLAY OFFLINE

Under that, I have three choices:

1. Latest Release 1.11.2
2. forge 1.11-forge1.11-13.19.2.2189
3. Corwin90 1.11-forge1.11-13.19.2.2189

When I try to play under any of these three I see the messages:

ERROR
Some game files are missing, and can't be downloaded while the launcher is in offline mode. Please connect to the internet and try again.

Why have a 'Play Offline' button at all if the game obviously can't be played offline?