What counts as dissolution/liquidation (C-corp)

I expect my C-corp to cease operating and doing business this year. However, we have not put into place a liquidation/dissolution plan (frankly am not sure whether we will be able to get to one before we stop operating). 

I have two questions:

1. If a corporation returns investment capital back to its shareholders but does not exchange it for stock is that still considered a liquidation? 

2. If my C-corp will stop operating but does not file an official dissolution with the state of incorporation (Delaware), do I still need to file a form 966? 

IRS: "A corporation (or a farmer’s cooperative) must file Form 966 if it adopts a resolution or plan to dissolve the corporation or liquidate any of its stock."