If you go by another recent Consti Bench decision in CBI v RR Kishore, removal of immunity operates retrospectively. So yes Sita Soren if it allows prosecution is likely to be retrospective.
All this of course assuming there is some actual evidence provided of MM's bribe taking. So far only statements have been issued by various parties.
What happens if there's a verdict in Sita Soren that changes the position of law. If MM's case is decided only afterwards (provided Sita Soren allows prosecution for bribe-taking), she'll be in trouble, right? Unlikely that Sita Soren will work merely prospectively.
All this of course assuming there is some actual evidence provided of MM's bribe taking. So far only statements have been issued by various parties.
https://theprint.in/opinion/mahua-moitra-has-constitutional-immunity-even-if-she-took-bribe-she-cant-be-prosecuted/1811750/