Has anyone in here ever filed an election to terminate a consolidated return?

Do you need to? If each becomes an S Corp, they are not eligible members of a consolidated filing group.

I am completely clueless about this, and hopefully Susan is right and it would be automatic, but ...

Regulation §1.1502-75(c) is where it mentioned that election, and you must have "good cause" un-consolidate them.

https://www.law.cornell.edu/cfr/text/26/1.1502-75

It says you need permission, and based on this PLR, it seems like you might need to do a PLR, which is challenging and expensive.

https://www.irs.gov/pub/irs-wd/0944014.pdf

I believe @sjrcpa is correct. If you look up consolidated tax return definition it says. Note the bold " until the affiliated group terminates"

Electing to File a Consolidated Tax Return

Each affiliated corporation must consent to file a consolidated tax return by filing Form 1122 and returning it along with Form 1120, the tax form for U.S. corporations. After that point, any new member of the associated group must join in the consolidated tax return. Single affiliates may leave the consolidated group without the group's status being terminated. The election to file consolidated returns can be difficult to revoke for the group. Once made, the choice remains binding on all subsequent tax years until the affiliated group terminates. The Internal Revenue Service (IRS) may grant permission to discontinue the election.