You can use an http action in sharptools to check the offline status of a device.
HTTP GET
https://api.smartthings.com/v1/devices/DEVICE_ID/health
Authorization: Bearer YOUR_PAT
You can get a PAT here: https://account.smartthings.com/tokens
You can find the device ids under the location>thing details from the sharptools page where you see and manage locations. Would like to check device every XX minutes for offline status - #28 by josh
Then you can set a variable using the $context.response.data.state or use it in a condition or concat a string together or whatever. Could be a neat case for expressions
Heres the original discussion Would like to check device every XX minutes for offline status - #18 by IslandSoul