[Trivial Psychic]

So I finished playing the latest Port, which I haven't done in years, and in the last mission, that is, the one following the destruction of the Lucifer when you arrive in Sol, and I detected a non-target-able friendly object.  When I went to investigate this object, I found that it was somewhere within the hull of the Arcadia.  What is it and what is it's purpose?

[Galemp]

It's a stealth Loki named 'Instructor' which must be present in retail missions if you want to send 'Training' style messages such as the credits you see there.

[Trivial Psychic]

What would have happened if you'd done a ship-vanish just after the mission began?  Does it have to be there for as long as the training messages are playing?

[Galemp]

Dunno, never tried it. AFAIK the Instructor must be present for training messages to appear.

[Goober5000]

Does it have to be there for as long as the training messages are playing?

For as long as you send them, yes.