"When kolto was replaced in favor of bacta, the Republic abandoned Manaan, and the Selkath left Ahto City for their ancient cities in the depths of the planet's oceans. Manaan did not have further contact with the galaxy until the Selkath were enslaved by the Galactic Empire sometime during the Galactic Civil War."
"Bacta was invented by the Vratix on the planet Thyferra in antiquity, with the galaxy at large learning of its properties around 4,100 BBY."
4,100 BBY = Year 447 before the Treaty of Coruscant (BTC)
Sorry man, probably no Manaan :/
4,100 BBY was more than 100 years before KotOR, which first introduced Manaan and Kolto, so even if that's when the galaxy started using Bacta, it's doesn't look like that's when it replaced Kolto.
The timeframe for Kolto finally getting phased out is still up in the air, and they could even use this game as an opportunity to expand the story of how that change happened beyond just "Bacta was better".
Personally, I'd really like to see Onderon/Dxun.