Undisturbed planetary alignment after galactic collision How do planets still orbit around the empty space where a black hole was after a black hole absorbs the milky way's black hole and keeps moving through space without disturbing surrounding planets that were orbiting that black hole?
The short answer is that they don't. If an even larger SMBH passed through the centre of the Milky Way and "swept up" the existing SMBH, all the stars and planets that are close to it (within a few tens of light-years, maybe more) would experience huge disruption and might end up orbiting the new black hole and being carried away, or flying free, or whatever.

The stars and planets much further away, which make up the bulk of the Milky Way wouldn't be much disturbed, because they are held in their orbits by their gravitational attraction for each other, and for the dark matter halo which suffuses the galaxy and only a small contribution comes from the gravity of the SMBH.