[Update: the issue seems to be resolved, as I am able to start the (hitherto unpatched) game from the launcher without problems or without the launcher trying to download a patch. Regular patch day should follow suit on Monday/Tuesday (EU).]
Edited by KhajitFurTrader on November 9, 2014 2:32PM
If your client hasn't been patched yet, or you've restored it from a backup, you can circumvent the Launcher for the time being, and launch ESO directly from
/Applications/Zenimax Online/Elder Scrolls Online EU/game_mac/pubplayerclient/eso.app
Just remember to use the Launcher again after 1.5.3 has been officially released, in order to patch your client to the latest version again.
If your client has already been patched erroneously, and you're using Time Machine (or some other backup solution), you can delete the Zenimax Online folder from /Applications, and then start the Time Machine app from that location in the Finder. Go back to yesterday evening (there should be hourly backups im TM), and restore the folder. Then launch the game from the eso.app described above.