A reasonable guess would be that the gravitational waves coming off would be similar to those of collisions of two neutron stars or two black holes. People who actually have run computer model simulations of these collsions say that this is indeed what to expect, waves a little weaker than from a collision of two black holes. See
http://newscenter.lbl.gov/2017/08/02/new-space-simulations-neutron-star-black-hole-mergers/
http://newscenter.lbl.gov/2017/08/02/new-space-simulations-neutron-star-black-hole-mergers/
Mike W.
(published on 05/31/2018)