I'm editing a story right now, and they use this construction with no speaking verbs a lot:
Rachel was finishing washing the dinner plates, “I know this will be hard on them, but Shelby needs to go on home."
I know you could replace that comma with a period, but I wonder if it's common to use a comma or semicolon to avoid slowing the reader too much?
This next one makes more sense to me because laughing could conceivably be a speaking verb:
Maddie's laugh was laced with sarcasm, “Mark, looks like you’ve got a friend.”
That one could even be a colon...
Am I overthinking this? Should I just replace them all with periods?
Based on common prescriptions of grammar: it's best to use periods.
Based on what I'd write if I were in the author's shoes: I'd either rephrase the lines or use period-dashes.
Based on how I'd feel reading these lines in a novel: the commas are fine.