My prediction:

The charter will be upheld, but only as amended by the voters in November. The Court will find a clever way to conclude that the effective date of term limits will be tomorrow, the day the decision is made official. That will mean that the term-limited officials already sworn in will be allowed to serve out this term, but that's it. There won't be a special election to kick the bums out. The drama will subside fairly quickly.

--Socialist With A Gold Card

Part I: There's a whole range of possible results.

From one end:

charter invalid, everyone stays in office because there's no term limits

to the other end:

charter valid, everyone (commission, clerks, register of deeds, sheriff, etc.) out.

But you might get a blend of the latter, with only some getting put out. If anyone goes, my guess is that it certainly will be commissioners.

Part II:
If the latter is decided, then there's the issue of when the office holders must get out.

On one end: term limits start now, so everyone now has two terms, starting now.

On the other end: everyone out as soon as your replacements are appointed at this month's commission meeting.

In between possibilities: you can serve out the present term (commissioners and sheriff then have almost 4 years left; and some clerks have a little less than 2 years to go), to the seats are up for grabs a) in a special called election, b) when the next regularly scheduled election is held (city election this fall, next state election next year, I believe).

Feel free to add possibilities, they are probably almost limitless.