We’re working on new gateway side status tags (that can be alerted and historized) for 7.3. Unfortunately, until then your options are a bit limited.
For detecting that the device is down, your best bet is to alert on the quality of a tag from each processor. Create an Expression tag, whose expression is simply a reference to the “.Quality” property of another tag. Create an alert on it, and alert when != 192 (the “good quality” value).
For redundancy, unfortunately I’m not sure there’s much you can do right now. There is a scripting function for getting the current host ip, perhaps you could use this (though an expression and runScript()) to log to the database with a transaction group… and then work up something that watches that and alerts when the last entry wasn’t from the normal master. A bit crazy, I know, but like I said, we’re working on it.