You should never leave chocolate pie out overnight at room temperature or any other pie for that matter.
When you leave the chocolate pie or any other pies out at room temperature bacteria can easily and rapidly grown on the pie and cause illness if you eat the pie when it's been left out overnight.
Pie should never be left out at room temperature any longer than 2 hours and if you're not gonna eat the pie including the chocolate pie within 2 hours be sure to refrigerate it to keep the bacteria off the pie.
The pie should last in the refrigerator for 3 to 7 days but it's best to eat the pie within a few days for the best taste and freshness.
Never leave any pies including your chocolate pie out at room temperature longer than 2 hours because it can contain bacteria.