Crust: Combine Oreo crumbs and butter; press into and up the sides of a greased 9-inch deep-dish pie pan. Freeze until firm.
Chocolate Sauce: In a small saucepan, melt the chocolate and butter over low heat. Stir in sugar gradually. Add evaporated milk in three additions, whisking until smooth. Remove from heat and stir in vanilla.
Let cool completely in the refrigerator. It should thicken but stay pourable.
Assemble Pie: Soften the ice cream slightly and spoon into the frozen crust. Smooth the top. Freeze until firm (about 1 hour).
Spread half of the cooled fudge sauce evenly over the top of the ice cream layer. Freeze again until set (30–45 minutes).
Spread whipped topping over the fudge layer to create a creamy “frosting” that seals everything together. Decorate with whipped topping by piping swirls or dollops. Alternatively, you can just cover with plastic wrap and put the whipped cream on each slice after cutting.
Return to freezer and freeze until very firm, at least 2–3 hours or overnight. When ready to serve, let stand at room temperature or in the refrigerator briefly to soften. Cut with a sharp knife dipped in hot water. Garnish each slice with sprinkles, nuts, and cherries. Pass the remaining fudge sauce at the table (or you can put it over the pie before slicing).