Do the enemiez in arcjet ever respawn?

Probably. The game has Radiant 4 dynamic AI driven automagic quest generation technology* that just works.

Not very well ...but it just works....

And it probably triggeres a respawn at some point.

* as opposed to that clunker Radiant Skyrim randomly cludged together mess that just bairly worked, when it did not randomly break the real quests, and did nothing we tried to hint that it did