Greek voters appeared to decisively reject a bailout deal offered by the country’s creditors two weeks ago, an outcome that could redefine the country’s place in Europe and shake the Continent’s financial stability. The no vote would be a triumph for Prime Minister Alexis Tsipras, who had campaigned for that as a way to give him more bargaining power in negotiating a new deal. But it also raised the possibility that the creditors would walk away, leaving Greece facing default, financial collapse and expulsion from the eurozone — and even, in the worst case, from the European Union.