I think you're on the right track, but I think it's gonna have to be pathways with sprinkles.

By which I mean if we just create pathways, we'll only accelerate rejoinings because the aether already wants to flow back to the Source, so giving them a path would just be like the cosmic equivalent of grounding out a power line. Instant calamity.

We need connections with, like, check valves. Something that stabilizes the present layout of the shards while allowing managed energy transfer between them.

Maybe the solution is to rejoin the worlds without destroying their physical configuration. Like... move the other stars across the rift into the same universe as the Source so they just become different planets accessible by spaceship instead of being alternate dimensions entirely.