Rypara is well suited to its name reflecting its liking of water although it is fine in usual garden conditions. It is a pleasant enough salvia with spikes of small mauve flowers on 1.5 m stems but it suckers around which might be enough to be annoying.
It is evergreen but old stems can be slashed to the ground anytime to invigorate it. It would not be easy to accidentally kill an established plant. It is frost hardy.
It sets seed but you could also pull up a sucker.
Usually available. This is winter dormant so please check whether the plant is good to post at the time you are ordering.