That's all really interesting, thank you! Yes, I recognise these sorts of things from eighteenth-century books—and the 'fixed position verb' thing from Swedish, which still has it. And I still say 'is gone', though I wouldn't do that with most verbs—'is returned' sounds not wrong but very old-fashioned to me. Thanks for the link too!

Something else I occasionally see in period books (including Tristram Shandy) is 'you was'—not 'you is' or any other singular verbs with 'you', so it sounds quite strange on its own. But I wonder if the 'where was two young men' there is a version of the same thing?