That would give you President Biden.
Unless Obama were impeached and convicted, Biden would be VP. If Obama never qualified after becoming President-elect then Biden becomes Acting President but not actually President. I don't know if a presumptive President or a President elect can be impeached, but I don't think so. If 'President elect' is considered a 'civil Office' by virtue of being explicitly mentioned in the COTUS then I suppose so, but that is really, really stretching the definition. A gain, as Impeachment is limited to 'The President, Vice President and all civil Officers of the United States' I don't think the President elect can be impeached.