Someone asked a question about this on Twitter, and [Jeremy Crawford responded][1]:

> *The spell Summon Demon's material component is blood from a recently killed [humanoid]. If that [humanoid] is revived would the spell end, a circle of the blood no longer grant protection or would it the person still be considered killed in the last 24 hours.*
>
> **If someone is killed and then revived, being revived doesn't change the fact that they were killed.**

Of course, the DM could probably reasonably houserule that the spell might work slightly differently or less effectively if the "killed" creature were then revived.


  [1]: https://twitter.com/JeremyECrawford/status/1060593419230294018