Well I think from a constitutional standpoint, this whole thing has shown a light on the curious overlap of executive and legislative (and judicial). From the broadest possible view, this system has worked somewhat; it has got Britain to where it is: prosperous, safe and stable. And when you look at The Wall fiasco in the US, or the Civil War, or gun control, we can't be too smug about codified constitutions.
Miller stated plainly that when rights are concerned treaties are a legislative function. And that as rights are affected by Brexit, Parliament is ultimately responsible. This was taken care of the next day by a quick bill, but with the meaningful vote question still muddying the waters. If we had a codified constitution instead of a jumble box full of velum we might have some clarity.
To me, the meaningful vote was when Parliament resoundingly rejected May's "plan". And May knew it was going to be rejected for quite some time, probably from the beginning. May should have, by any measure of reason, resigned at that point (though since she always knew it was going to fail, she probably should have resigned much earlier).
I think that this "going back to bargain again" is clearly against the spirit of meaningful vote, as any vote now will take place on the edge of a cliff. I say "spirit", as I don't think there is any mechanism for the courts to step in. At any rate Parliament, and the parties, have certainly been complicit in not giving any sort of guidance as to what alternative would pass a meaningful vote.
I welcome a second referendum, but can't help feel that it will be hard to avoid the problems associated with the first one. A better idea would to be to admit the first one was deeply flawed and either cancel this madness completely and forget about it, or cancel this madness and set very stringent requirements for any following referendum. A plan for instance. Detailed analysis. Something other than some crap written on the side of a bus.
Further, I think that no matter the outcome, we need a constitutional convention of sorts.