Yes, Magic Online is available again. Our apologies for the frustration and inconvenience of this crash.
If you were in an event prior to the crash, it will not continue. You will need to file for a refund. Please go to accounts.wizards.com and login. (This is separate from your MTGO login, create a support if you do not have one.) Then Click here to go to the bug report form to file a refund. (For a refund you keep your cards and get the cost of entry back.)
You will need your event ID to file a refund. To find it, open your Deck Editor, and hit Load Deck. Click the Look In drop box, and select Default (even if it is there already), and go to the Tournament Decks folder. The deck file that is saved there has the event ID, it is the first number listed in the file name.