If I move Akali, Deadly Weapon into a battlefield with Mask of Foresight on board and then ambush in Morgana, Vindictive and then move Akali back out with my Akali legend, does Morgana get the 1 might from Mask of Foresight?

No, Morgana does not get the +1 Might from Mask of Foresight.

Mask of Foresight's trigger condition ("when a friendly unit attacks or defends alone") is checked only at the moment that unit gains its attacker/defender designation — it does not re-check if the board changes later (FAQ #6385, #5554).

Here's the timing breakdown:

1. Akali moves in → Combat Showdown begins. Units are designated: Akali = attacker, defending player's original unit(s) = defenders. Mask checks — no one is alone.
2. Morgana is ambushed in as a Reaction. She gains defender designation during the cleanup after her play. At that moment, Akali is still there, so Morgana is not alone when designated — Mask does not trigger.
3. Akali is later moved to base via the Akali legend. This removes Akali from the battlefield, but Morgana already has her defender designation from step 2. Moving other units away does not cause re-designation and does not create a new Mask trigger (FAQ #5554, #4644).

Since the "alone" condition was never met at the moment of designation, Mask of Foresight does not trigger at all for Morgana in this scenario.