It depends on the time period, of course, but much of NATO strategy was about the use of tactical nuclear weapons to offset Soviet military superiority. So in NATO's mind a conventional WW3 would be a loss for them — they thought they would likely initiate nuclear use, and indeed their entire force posture was set up along those lines. Whether such nuclear use would stay at the "tactical" level, or whether it would escalate to "strategic" nuclear war, would depend on the specific planner you had in mind (some thought it could be contained, many thought escalation was likely).

I have no idea if the Soviets contemplated a scenario that would not escalate to nuclear use quickly, but I suspect not. The idea that either side would be able to resist using these powerful weapons in at least a tactical way seems to have not been very common.