Ludevic, Necrogenius // Olag, Ludevic's Hubris

Olag remains a copy of the creature card you choose even if that card later leaves exile.

If there are no creature cards exiled with Ludevic as it transforms, perhaps because those cards were removed from exile in response to its activated ability or it transformed another way, Olag won't be a copy of anything. Olag will simply be its 4/4 self with no +1/+1 counters.

It's possible for Olag to become a copy of a card with the daybound keyword ability as it transforms. If this happens, it doesn't transform as it becomes night.