It depends how deep the water is, but I've had them survive in very waterlogged ground for a significant amount of time, about a fortnight as I recall, although this was in winter. By the way, there is an easier way of solving the problem of "rose sickness" - a product called Rootgrow, which is beneficial fungi that you mix into the planting hole; they encourage root growth. I've read that rose growers have successfully planted one rose in the space that they've taken another out of using this, with spectacular results.
