Yeah it's hopeless at that point so the regs cut anyone doing practice IFR without a safety lots of slack (kidding).
No one flies in IMC without being on an instrument flight plan under ATC control and usually also with radar surveillance. Even when you are off the ATC radar you are able to use your instruments to hold course in the clouds, and the risk from not being able to see other aircraft is addressed by all aircraft being either under active vectoring by ATC with radar, or by them having a unique cruise altitude they must abide by. One aircraft overtaking another in the same direction on the same route in IMC never happens because although there may be no radar supervision, ATC would not approve the same flight level for two aircraft at the same time over the same route. As a last case backup there is TCAS (onboard Terrain and Collision Avoidance System) in case someone is both off radar and (way) off their assigned altitude. In any case, a safety pilot is not used, but the regs state that in IMC the pilot in command must try and see potential sources of collision ("see and avoid" policy) anyway.
By the way, the rules for flight by instruments are written in blood by historical disasters such as
this one