The thing is, aborted timelines are doomed. Like, inherently. Unless you manage outright time travel(and I view Undertale's RESET as more akin to that than hopping timelines) then you have a very small window of time before it collapses into non-existence. In normal Materium conditions(at least with 4 Chaos Gods instead of 5 or more) this happens in moments at best, instantly at worst. In the Warp, they can exist indefinitely, but are chronologically and thus conceptually fragile and if observed by a Materium being could collapse even if they are in the Warp, hence Daemonic Incursions aren't auto-wins because Daemons can't freely wander in places with mortals if their timeline is compromised.
On a Warp-touched world, items and the like from alternate timelines might bleed through, but they'd likely have very limited lifespans, and their destruction would have Balefire-like effects. That is, not only would they cease to exist, but their effects would be unwritten. A wound from a blade sunk into non-existence didn't disappear, it never happened, beyond some faded memories from any soul-bearing witnesses, or more vivid ones with Psykers, though Power Weapons and the like could resist to some degree, they too would have the punch taken out of their actions, with it growing exponentially the further back from dissolution you went. Abusing it would essentially require a ridiculous Psyker like Serras or at least a Gamma to intentionally create thinking beings, even if copies of themselves, doomed to a quick death. Like, literally within the week even for the former. Chaos can't really take advantage of this because they're to a man selfish bastards who are as likely to try and kill the bastard who did this to them, and Serras would find the idea morally repugnant. The idea is essentially that world is weird, and could have implications for research into improving the C.A.T. due to knock-on effects from understanding the temporal implications of Warp tomfoolery, but would be unlikely to directly offer much benefit beyond a small pool of Psykers experienced in temporal nonsense, as chronomancy is normally fairly restricted in terms of numbers.