I agree with Edwin Ashworth that running the quotations as a series of parallel clauses in a single sentence does much more harm than good to the coherence of the final product. Instead of doing that, I recommend getting rid of the "et cetera" at the end of the original sentence and running each quotation as a stand-alone example:
The worst scenario is when your friend refuses to bear any responsibility for the cancellation: “We weren’t really sure we were meeting tonight, were we?” “Good thing I see you all the time anyway.” “I know you understand how demanding my job is.”
If you insist on retaining the original one-sentence approach, I advise punctuating it as follows:
The worst scenario is when your friend refuses to bear any responsibility for the cancellation: “We weren’t really sure we were meeting tonight, were we?”; “Good thing I see you all the time anyway”; “I know you understand how demanding my job is”; et cetera.
The first time you use a semicolon in that series of quotations, you establish the semicolon as the standard mark for binding each of the parallel pieces in that sentence to the others.
Your argument that including a question mark at the end of the first quotation justifies including a period at the end of the second quotation (and a comma at the end of the third one) ignores the special status of the question mark as an unusual end-of-sentence marker, whereas a period is the default (and assumed) end-of-sentence marker. That special status helps explain why a comma can replace a period at the end of certain quotations ("It's too confusing," he said) but can't—or at least usually doesn't—replace a question mark ("Is it too confusing?" he asked).