You'd only initiate the pull-up if you had full power from start of roll to pull-up. Engine failure at any point during the couple of seconds of vertical flight (I must empasise, I only hold the vertical for a couple of seconds - the aeroplane is probably capable of maintaining it for at least twice that, but I'm not good enough or too cowarly to push it anywhere near the limits at low level) would require an early push-over or roll out, to a standard EFATO.
Experimenets at altitude indicate that complete power loss at the point of pull-up would still allow a reasonable vertical section to be flown before the need for a push-over, such is the Yak's inertia. At low level, a power failure at the point of pull-up would be handled by trading speed for height in a staright-ahead climb, then standard EFATO.
SSD