Many people have the same question, in fact I think it was just asked last week again.
The short answer is that there isn’t anything you can do just with smartthings to handle this. But there are standalone Wi-Fi devices which can detect when they themselves have lost contact with the Internet and then reboot on a schedule that you set. Or just reboot once a day or something like that.
You can look on the quick browse list in the community – created wiki look down towards the bottom of that page for the project report section, and then look on the list for power projects to see how other people have approached it.
Or just look at the following thread, which discusses three or four of the different Wi-Fi plug options.