Evolution of an example binary system with = 20 M_⊙, = 15 M_⊙ with P^ZAMS = 100 days, described in Sect. 3 (see also the cartoon in Fig. 1). Top panel: primary, secondary, and total mass. Bottom panel: orbital velocity of the secondary (left y-axis) and period of the binary (right y-axis). The labels indicate the following phases: A. the MS of the primary, B. case B RLOF, emphasized by the vertical dashed line, C. the binary is made of a He star (possibly looking like a Wolf-Rayet star) and a rejuvenated MS secondary; D. (and the vertical dot-dashed line) marks the explosion of the primary in a SNIb/Ic which unbinds the NS and its companion. During the phase E1. the secondary is a slow moving walkaway star, traveling for a duration of about half the main sequence lifetime of the primary.