Paramount and Cedar Fair didn't overlap outside Ohio. The merger killed Geaugua Lake. A Six Flags/Cedar Fair consolidation basically gives the combined company a monopoly on major regional theme parks. It's the equivalent of Disney acquiring Universal and Sea World Orlando.
Either parks get sold/shuttered, or "New Six Flags" raises prices significantly to cover debt. Granted, DoJ rarely considers public benefit as a condition any longer.
I expect to see bankruptcy, or sale of significant real-estate assets to pare down debts, if this merger happens. "Lease back" will kill the company.
If I'm a city with a Six Flags or Cedar Fair Park, I'd start suing to block this merger immediately. Tax revenue and seasonal job loss will effect them.
If I'm a customer, expect ticket price increases and an end to "cheap" season passes. Truthfully, Six Flags should have ended the latter decades ago.