What happens when a function that returns an object ends without a return statement

What gets returned?

We don’t know. According to the standard, the behavior is undefined.

ยง6.6.3/2 The return statement
[stmt.return]
:

(emphasis mine)

Flowing off the end of a constructor, a destructor, or a function with a cv void return type is equivalent to a return with no operand. Otherwise, flowing off the end of a function other than main (basic.start.main) results in undefined behavior.

In fact most compilers would give a warning for it, like Clang:

warning: control reaches end of non-void function [-Wreturn-type]

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