Thanks for writing. I'm so sorry to hear about your loss! That sounds terrible. The good news is that depending on how thoroughly your husband sprayed, some of your perennials may come back --- especially if your perennials are well-established and have been in the ground a few years. Unfortunately, any annuals you had probably will not come back.
There's nothing special you need to do to the soil --- just wait and be patient. You should be able to replant in about 6 to 7 weeks without ill effect from the product.
---Justin, Senior Garden Editor, BHG.com