Enroute Controller providing OJT and wanting to allow the developmental to catch a route error; reported a restricted airspace entry event.

Narrative

I was training a transferring CPC at R73. Traffic was light and we were working the sector alone. Aircraft X was being handed off to us from ZZZ2 Aproach. His route of flight was ZZZ2..ZZZ3.. etc. at seven thousand feet. I noticed that this route would take him into ABCDE2 and ABCDE3 which were hot to eight thousand and flight level two three zero; respectively. As a training opportunity; I waited to see if my trainee would catch this bad route. Aircraft X checked on frequency and my trainee acknowledged. My trainee then went around the sector and did several other tasks. I waited for a little bit; and then put a route line up on the scope; so that he could see that the aircraft was headed for the restricted area; which was drawn on the scope. He didn't catch it. My trainee started to hand off Aircraft X to ZZZ1 approach; which is where ABCDE is located. I stopped him at this point and flatly told him that he had to route him around the restricted area. My trainee cleared him direct ZZZ1; direct ZZZ3; rest unchanged. Aircraft X didn't answer. My trainee went on to do something else; and I overrode him and tried again to call Aircraft X to no avail. Aircraft X had gone NORAC. We tried through multiple transceivers; and had other airborne aircraft try to raise Aircraft X with no luck. I called ZZZ1 Approach and told them what was happening. Then I immediately talked to the supervisor and told them that I had a NORDO aircraft headed towards ABCDE; and that I needed them to call the range to stop their activities. We repeatedly tried to contact Aircraft X; still no answer. As Aircraft X entered approximately 2 miles into the restricted area; he finally answered a radio call. I immediately turned him due West and climbed him out of the restricted area. I told the pilot that we had made multiple attempts to contact him; but he claimed that he had heard none. We then handed him off to ZZZ1 Approach. Recommendation; the aircraft went NORAC after checking on. The guy just quit listening to his radio.