I don't see the potential problem in this cse.
Relays are generally made with the contacts mechanically coupled so that one pole cannot stick without the other sticking. In this case, even if the direction DPDT was implemented with two separate relays and one failed, the load would simply see no voltage.
Shorting from N.O. to N.C. contacts (what, I think, you are worried about) is not a normal failure mode of a relay. The contacts are attached to the same bit of metal that swings back and forth, so even if the relay is abused by a surge current or the contacts eventually wear out they will never short N.O. to N.C.
Now, we can imagine a pathological situation where such a short does happen- maybe the 3rd shift operator fails to crimp the contact into the spring adequately and it falls off, rolls around and makes the short we're worried about. Okay, there's a short. It's not a particularly "bad" short, it's just a short- same as if some idiot poked a screwdriver across the wires. The other relay closes (probably damaging it by the surge) the (properly sized) wires experience a brief surge in current, and the properly rated fuse or circuit breaker (not shown) opens, safely interrupting the fault current. Service personnel diagnose the fault, replace the bad parts, and all is well.
You must have the proper fusing (rated to carry the load current, to interrupt the maximum fault current, and for the maximum source voltage) and proper wire sizes (surge capability is built into the recommended minimum wire sizes) for safety even with no relays in there, so that is a non-negotiable requirement.
I have not considered any potential safety situation with the motor sticking "on" but you may wish to add some redundancy to prevent that from occurring (perhaps another SPST relay or replace the DPDT with two SPDT). In that case, you might have to add a feedback input to the PLC to detect potential sticking because otherwise you would not know service was required until the second failure (which could be an unsafe condition). A better solution would be a big red mushroom-top emergency stop button rather than anything involving the PLC!