Honestly Kat they probably just moved. the nest are designed to avoid being flooded and if the nest is compromised by flooding they will move to a new area. Each nest will have two entry or exit points so they probably went out the back. Many many people will say don't use gas because it will contaminant the soil but it works and works well and from what I can tell my soil is fine. I think too many people go overboard with the gas and that's the main problem. Like I said before an 8 oz glass will do the job but it has to be done at the right time.
When I was a kid I tried boiling water and got stung several times so please don't try that. wasp spray don't work because of the way the nest is designed you'll only spray in the soil and they will most likely come out the other hole and get you. a powdered Pyrethrin insecticide has been known to work but it's a slow process and pets and kids can get into it. The only other options are hiring a professional which is costly but if you have the funds by all means go for it. In the mean time I'll stick to using gas when I find them.
