Genshin Impact leak suggests that once the Genshin Impact version 2.5 update rolls out, the Bathysmal Vishap Herd will gain the ability to revive.

Version 2.4 introduced us to Enkanomiya, a mystical area beneath Watatsumi Island in Inazuma. Within Enkanomiya rests the Bathysmal Vishap Herd, a new field boss. While it is challenging as it is, it seems like it would be more difficult come Version 2.5. The Bathysmal Vishap Herd, aside from being a field boss, is in Version 2.5's Abyss lineup. This version of the Bathysmal Vishap Herd has the ability to revive the other if not killed within a certain timeframe.

https://twitter.com/Ubatcha1/status/1480700207977353224

The Three Realms event mentioned is an event that will show Travelers a different version of Enkanomiya. It seems the buffed Bathysmal Vishap Herd will also be present during that event. The silver lining, if you will, is the fact that it doesn't revive with full HP. This tweet suggests that the window of time you have before the other one revives is around 10 seconds. The defeated Bathysmal Vishap will remain on the field lying down, with a visible link to the still-alive Bathysmal Vishap. It seems evening out your damage across both Bathysmal Vishaps is the way to go with this buff. Whether this buff applies to the field boss in Enkanomiya or not is unknown as of time of writing.

In the meantime, here's our guide to defeating the Bathysmal Vishap Herd, since Yae Miko requires the drop from this boss.