Former Ph.D. student Ylva Götberg (now Nashman theory fellow at Carnegie observatories) estimated the relative contribution of massive stars, stars stripped in binaries and active galactic nuclei to the epoch of reionization. We estimate that stripped stars contributed tens of percent of the photons that caused cosmic reionization of hydrogen, depending on the assumed escape fractions. More importantly, stripped stars harden the ionizing emission. At high redshift, stripped stars and massive single stars combined dominate the He II-ionizing emission, but we still expect active galactic nuclei drive cosmic helium reionization.
Götberg, de Mink, Mcquinn et al. (2019, A&A in press)