However my issue is that the rest of the sketch - the remainder of set up and loop- will not run.
Maybe you should post that sketch.
have yet to find out what happens when the DHCP server decides the lease is up and someone else takes the address in the mean time. reboot solves all but I am putting in sensors on a remote locationand hope to have reliable connection for 30 days at a time...
No, that is what Ethernet.maintain() is for.
Until half the lease time is expired, this does nothing and returns 0 (nothing happened). After that, it renews the dhcp lease just like it supposed to. I checked it. It works. I call it once every 20 minutes, but I don't see why you couldn't call it more often than that.