On boxes with similar reliability requirements, we would make "educated guesses" as to whether network interfaces might need a reset. Issued a "send packet" command and not seen a "transmission complete" back within 5 seconds ? Reset the interface! Not seen ANY received packets in the last 10 minutes, when you expect to see one every 10 seconds? Reset the interface! Got some weird error status? Reset the interface!
You can consider doing this for your entire project, of course. The "penalty" for resetting an embedded cpu like an arduino is a lot smaller than for a mainframe or desktop system, and rebooting every 24 hours might hide a lot of weaknesses in your software that might show up in 25 days when millis() turns negative (for example.)