By law, the deadline is "before the European Parliament decides whether it consents", conceivably too late for the meaningful vote to be, well, meaningful.
Until it happens, no "plan B" vote under s13(6) is required
But their combined target is: no more votes; and too late and/or with no voice for the Commons if there are any.
That WOULD qualify as a constitutional crisis, I think.
Anyway, Good night.