Certified GKH Gardening Expert
You can remove the spent blooms of salvia or even take them prior to full bloom to help prevent any re-seeding if this is an issue for you.
I have grown Victoria blue salvia for years. If you leave the plants in the ground in the Fall till they are dried up a bit or frost has killed them they will drop seeds and the following Spring there will be hundreds of new plants growing where you had the old plants. You can then dig them up when several inches tall and relocate them.