I'd be extremely interested in getting re-emergence to work, and to centralize all research for it in one thread.
Why does emerge_faction not suit you?
Your "give region to faction" might work, if you make England unkillable as a faction. Currently a faction with no provinces or leaders simply disappears from the game, but there are settings for Mongols which specify them as alive even if they have no units or regions, so that they can emerge later on with additional hordes.
The same principle should apply here. What you'd basically have is a script monitoring the 4-5 key english regions... basically all of Brittania and maybe Normandy.
Code:
If faction england has < 1 region,
And if region X has low happiness,
Give region X to England,
Spawn a small army
Code:
If faction england has < 1 region,
And if region Y has low happiness,
Give region Y to England,
Spawn a small army