So, there are several things at work here. The short answer is that after one hour the first object vanishes as if it never existed. Automatic spells that cast what would normally be a daily upkeep last an hour. That aside. There is a certain order to how things happen here.
They go as follows:
- The Spell triggered (somehow).
- Charges decrement.
- The item that you target is seen, and everything about it at that moment in time is noted down. (The Presence is critical here)
- After this, it finally would have the copy made.
Additionally, as Imitate would be a level 2 power for an artifact, the item in question needs a minimum of 15 presence to even hold a level 2 power. It then increases its presence by that same number, to total of 30 presence. This remains within the capabilities of the Imitate spell.
With all this known, because the object is actively maintaining the spell it would behave identically to the case of a wizard suddenly vanishing.