Could untreated clinical depression escalate to bipolar?

Maybe: Most depression remains unipolar, does not become bipolar, if not treated. Bipolar disorder commonly has, as a first episode, a depression. If untreated, it can continue as depression, or resolve, or, less commonly, switch to a manic or hypomanic or mixed state. It can be very difficult to distinguish whether a first episode of depression is unipolar or bipolar. Best to consult a psychiatrist.