A min fuel plan would typically have an alternate ...
Not necessarily.
... so if you do use your variable reserve, you just start using alternate fuel, not fixed reserve.
You make it sound like you never needed that alternate fuel in the first place!
If you don't have that alternate fuel on board, then obviously you are eating into your fixed reserve (FR) and now need to declare a mayday or make a diversion - assuming you departed with the minimum legal fuel.
And if you do have that alternate fuel on board, then you are still, in effect, eating into your FR and must either divert or declare a mayday.
And here is something else about that alternate fuel: There is no variable reserve associated with it. Under these new rules, they stipulate that VR is to be calculated on "trip fuel" only. "Trip fuel" does not include the diversion to the alternate! Before this new rule, everybody included the alternate fuel in the calculation of VR!
My opening words in this thread called into question CASA's and ICAO's understanding of what variable reserve was all about. Everywhere you look in these new rules you spot evidence that they don't appear to understand
what it is and
why it is.