AFAIK Vollmer retired from voice acting in 2011. I don't know whether Sabat did anything that forced her to retire. Seems like she retired from voicing Bulma because she decided to persue bigger things.
Per
Dragon Ball wiki:
Idk how accurate it is, but it should be noted that I think many Kanzenshuu mods or posters, including
A particular dbz reddit moderator manage the site.
The person who might have been a casualty of the casting couch decline is Linda Young (Z Dub Frieza VA). As TheAlanEdgeHead mentions
Here,
Also sort of covered
here around 3 minutes in. I think she has addressed it multiple times in other panels. If you find any other clips, please link it to the farms.
I initially took it in stride, but given everything we've learnt so far, I wouldn't be surprised if Sabat did block her from the part if she said no to him or some other exec at Funi. Also, she still voices Fortune-teller Baba (who got about 2 or 3 episodes in Super with little dialogue) , so who knows.
What even is this timeline
The 2020 Olympics is still just under a year away, there's plenty of time to take the IP away if they wanted too. My guess is that if they did start discussing things with Funi, the rights might only be forfeited after episode 131 of super airs as they've already recorded lines for it or Funi will make frantic offers in order to keep it or Toei will let them keep it but with certain restrictions or rules put into place in the wake of this shitshow
EDIT:
Realized Meredith Mccoy was also not present during Kai's recording.
Post on Kanzenshuu seems to explain it. Also an uncertainty. Maybe she initially turned down Sabat but then accepted his offer afterwards or she really was unavailable during Kai's recording.