Sounds like a great friend!***:)* It's difficult to say if they will come back but they might.* Sometimes the tops of plants will die off but the roots still survive.* Generally, plants with silver leaves like full sun, good drainage and don't like 'wet feet'.* Make sure the spot where they are planted doesn't get overwatered.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.