Not exactly. Even going strictly by gun time, he could still accomplish most of what he's been accomplishing via chip time (sub 3 hour marathons). The main thing that would become more difficult is winning the master's division (since he would actually have to finish in front of his competitors. Still very possible via his methods, but more catchable by his competitors). The shorter races (5Ks) would be more of a challenge, but still possible depending on the course route - Boston 5k would still be possible if he took the immediate right off the course, went around the church, and waited until the finish stretch, cutting off 90% of the distance.
The big advantage of this is that it eliminates the need for an RD to disqualify someone. Kippy's most-used tactic simply won't work since he wouldn't get his 3-4 minute chip adjustment. Forcing him and his type to do all of their cheating at the front of the pack makes it much easier to catch them.
Even with gun time, if you consider he may be cutting off 20+ miles in some marathons, he could still cheat to a sub 3 (seemingly the main goal), still start in the back of the pack to avoid drawing attention to himself, and still re-enter the course near the finish. He would just have a few less minutes to kill while waiting to jump in at the finish.