To be honest, I don't have the latest update on whether Mang Tani is still with GMA. Maybe you can follow some entertainment blogs or industry insiders for the latest scoop.
It could be that the producers of 24 Oras 2023 had a different vision or casting choices that didn't include Mang Tani. Sometimes these decisions are based on various factors that aren't made public.
Maybe a new character that was introduced into the story specifically for this plotline. This new character could bring a lot of mystery and new storylines related to the pregnancy.
One possible plot twist could be that Tani Rey discovers she's pregnant during a really challenging time in her life, like when she's in the middle of an important mission. This would add a whole new layer of drama as she has to balance her personal situation with her duties.