Switched Capacitor Theory
I understand your problem....Surprisingly, in many books and other contributions you can find a figure similar to the one shown by you. But one important part is missing: The theory of such an S/C block requires that the output is connected either to a large capacitor (much larger than the switched one) or to ground. In most applications, however, the output is connected to the virtual ground provided by the inverting input node of an opamp (charge transfer to the feedback capacitor).

Explanation: The principle of the S/C techniques is based on a CHARGE TRANSFER from one capacitor to another one or to a current-processing unit. The switched capacitor must be discharged during one clock cycle. Hence, in nearly all cases, the Vout node is connected to the inverting input of an opamp) .

It is NOT sufficient to explain the S/C principle with an open output node.