Hardly, because they will only be proposing another referendum if their version of Brexit is voted down, and effectively only after a long, long, near 3 year process during which the Government's version of Brexit has been repeatedly voted down, no deal Brexit voted down, and other versions of Brexit not getting enough support in Parliament. Apart from simply cancelling Article 50, or a General Election being called, as McDonnell is saying the only way left open if no version of Leave is voted through in Parliament, is another people's vote, though I doubt that would get through Parliament either. I still think the most likely outcome is MayBot will bore her deal through eventually.
I agree with your conclusion, Oslo. May's rather poor deal looks increasingly attractive against the other options which cannot find a Parliamentary majority. If the EU time limited the backstop, I think May's deal would get through Parliament and everyone on both sides of the Channel would have certainty. But I don't think May will ever get her deal through with that indefinite backstop. A UK government cannot bind future UK governments in perpetuity.