We have just had the same problem in our new (to us) garden, full of weedy
herbaceous borders. I would cut them all back, dig them up, divide if nec.
etc. weed and improve the soil then replant. My reasons are that (a) with a
bit of luck (depending on where you live) they then may have a chance to
start to grow a bit and settle in before winter which will decrease the
chances of losing any (b) again with some luck you may find that any
weeds/weed seeds left in the soil start to grow and so can be spotted and
dealt with now rather than later and (c) it will be a lot more pleasant
doing it now than in November. I don't think that it is worth trying to hang
onto a few flowers for a few weeks and then risking messing up quite such a
major job as this. I would also cut them back before moving as this seems to
increase their chances of survival.

--
Hayley
(gardening on well drained, alkaline clay in Somerset)