Goodgulf:
And I have seen, in published novels things along the lines of:
"And that's that!" He said.
Rather than:
"And that's that!" he said.
The former would be correct if the speaker was the deity.
Concerning the later remark, there's nothing grammatically wrong with "and that's that!". You could quibble over starting a sentence with "and", but direct speech shopuld reflect what people actually say - and they DO start sentences with and, especially ones like "And that's that!". Moreover, it isn't actually a breach of any grammatical rule (at least this side of the Atlantic) to start a sentence with "and", only something frowned on by stylists. On occasion in prose, for effect it makes sense to do something against conventional style. Compare "You left your bedroom in a mess, you took my bike without permission, you rode out into the main road without looking and you swore at the motorist who had to brake to avoid you!" with "You left your bedroom in a mess. You took my bike without permission. You rode out into the main road without looking. And you swore at the motorist..."