Loaded the mod up with the SLP - Dyson Sphere Reworked mod to add Sun Orbit and Close Sun Orbit to the space map, then started a new save and used the editor to unlock just Vulcanus. With the algorithm, there is no direct route from Nauvis to Vulcanus, pathing would have to go through either Gleba or Sun Orbit. This is visible in the second screenshot on this mod's page. In this case, it can be resolved by simply discovering Gleba, but it would be possible for other mod combinations to result in an essentially bricked space map. No idea how to resolve this.

I believe this problem will likely be exceedingly rare, but still possible.

If it becomes a real issue, I would suggest one of my other mods, which solves the problem of planets having little structure to their locations: https://mods.factorio.com/mod/Tiered-Solar-System