WITHOUT the ground it gives around +/- 20V protection across the RS485 lines only, that's not enough to prevent damage on most devices.
WITH the ground it gives about +13V to -8V protection from both lines to ground, for most devices that would be adequate.
So removing the ground makes the circuit useless. There should still be a ground connection between the transmitter and receiver(s) for RS485 to work as it can only tolerate a limited common mode offset. RS485 is differential but unipolar, if the ground is reasonably good, a single Zener limiting the positive excursion should be adequate.
Brian.