Sentence Correction (SC) | Re: That the companies would merge was a certainty, though less clear were

C. The companies’ merger was certain, though less clear was when the merger would take place, who among the top executives the chief executive would be, and who, if anyone, would voluntarily choose to leave.

Only option C maintains the parallelism correctly.

The companies merger was certain,

1. when the merger would take place,
2. who among the top executives the chief executive would be, AND
3. who, if anyone, would voluntarily choose to leave.