This sounds more like a premise for maybe a digimon spinoff. Everyone has their destined partner and goes about their lives without any apparent need for one.
It does sound a bit weird. Also if this is the last servant...does that mean no one is going to be born in that world in the future? Maybe it's just an awkward summary. While it sounds odd...there have been Fate series that go to unusual places. Maybe it will be better than it looks at first glance.
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