How persistent is the Enemies flaw?

In the core ArM5 book, is the example of Darius of Flambeau.
He has a Flaw - Enemies (renounced magus and his lackeys).

We were nattering the other day, and are wondering how much story potential such an Enemy would be?
Obviously Darius would have to take a Season or two off to travel and execute the renounced Magus once he acquired clues to the target's location. But we kind of thought this might be a simple one-off event - they meet, and it is a fight to the death.
Possibly the Renounced Magus could proactively throw/sacrifice lackeys at Darius to cause occasional mischief before Darius found the enemy's hideout. But we thought this was, um, weak. In all, we came to the conclusion that Darius has a Flaw that won't last long.

However, what if the Renounced Magus is somewhere where Darius would have to break the Hermetic Oath to reach him? Say, in the court of a powerful mundane or fairy noble. Then the Renounced Magus would be relatively safe, yet able to remotely make trouble for his pursuer Darius.

Does that make sense, or is there something I may have overlooked?

Your approach sounds darn good. My suss is that flaws are fair game for stories and confronting issues for the characters; major flaws far more so. And until the flaw is resolved it’s open season. Some SGs replace one flaw with another too.
It should be either a goal of the character and a prevailing story.

For me that flaw is not only the fact that the character have enemies at character creation, but also that he is prone to get more. If he gets rid of his enemies, it will be a matter of time to acquire some more.

A Story Flaw is a way for the player to say: I want stories about this to involve my character. So, an Enemies Flaw means that, about as often as any other PC with a Story Flaw, there will be a story into which Darius will be forced by his Enemies.

The Story Flaw lasts as long as you want, like other Flaws; it's a troupe decision if putting in a lot of effort the PC will resolve it, or possibly change it for another Flaw. This should be unusual though, because by choosing the Flaw the player has made it clear that he keeps wanting stories from that source to hit his PC.

Crucially, Story Flaws are external stimuli. This means that they come looking for the PC, not viceversa; the viceversa are Personality Flaws: e.g. Vow (chasing down the enemy) or Obsessed (chasing down the enemy). So: the enemy lackeys might every so often contest a vis source, stir up trouble with the local nobility, harm a friend of the covenant etc. and Darius then must take action and solve the problem.