Yes, but then I didn't really worry about it. After all, the 1d8 is only a minor component of the healing done by
mass cure light wounds in Trayah's case.
You realise I don't really care if you roll for every creature or not, right... I just thought it was worth mentioning, as it's an unusual way to do it in my experience. Though now you've got me wondering whether you roll dice for every creature when you play in person.
Then someone using a weapon only has the option of an all-or-nothing effect with each individual attack. So I don't see why spellcasters should use a different system, just because their spell damages multiple opponents at one time.