What if Re:Zero's central theme is IMMORTALITY?
Look at it this way: so far there were shown several people who can avoid death one way or another, and in the novels, several more were actively trying to do it.
Here's a list with users who bear different consequences for their different methods of preserving a pattern known as them.
Subaru - endless loops of terror and suffering with the ability to redo future. I guess he will die once his time has come naturally.
atella - sealed away in a shrine, unable to die, but somewhat still able to manifest in the real world.
Felix - dude with a healing water magic so potent, he can even animate the dead, including himself.
Reinhard - his blessing of eternal fuck you grants him a wish every time he needs it. Yep, blessing of Phoenix because why the fuck not?.
Echidna - had been put in stasis\undead condition by Volcanica as a failsafe against Envy, can interfere with the real world, created hosts for herself to fill in but failed to use themyet.
WholeWitchingWagon - collected as wraiths by DonaDona, whole band of witches seems to have their personas and powers still intact and functioning in her dream world.
Aldebaran - a pecular one, instead of looping BACK in time to redo his way around a lethal obstacle, he seems to be hoopping FORWARDS to skip the killing attack completely.
Not exactly. His power seems to be a loop he can either use on himself or someone else. I'm pretty sure he's been noted to make guesses about how many times his victims have died, in such a way that suggests he's died a whole lot more.
Regulus - another time shenanigans user, as long as his throbbing veiny meat is inside some poor gal he can fuck you all over.
Pandora - the ability to twist and rewrite any real fact in a way that suits you seems bullshit enough, surely she can just keep herself forever-young and undig her own grave?
Betelgeuse -> body hopping
Capella -> regenerator
And also the clown who seems to have developed his own methods of body swapping\forced contract which works only in his dynasty. The nasty fucker once bred a completely magic inert Rooswaal to combat some fucker who turned magic against its user. And possessed her. And then completed his business as usual. Oh, the benefits of immortaliyty.