Re-reading my comment, I shouldn’t have said “impossible”. Yes, any theory that successfully quantizes gravitation will allow superpositions of gravitational wo

Re-reading my comment, I shouldn’t have said “impossible”. Yes, any theory that successfully quantizes gravitation will allow superpositions of gravitational worlds. String theory likely does this, though some will quibble with the phenomelogy as to whether it reproduces general relativity as we know it.