“ He will not be engaged in writing the GOP convention rules.”
That is not necessarily correct. He won’t directly but he will most likely have a significant number of supporters on the rules committee.
No Trump will control the rules committee. Cruz will be pretty much shut out as he is unwilling to even endorse the nominee or do anything to unify the party. The nominee runs the show. Most delegates will be eager to unite with Trump and put Ted in the rear view mirror where he belongs. Only a handful of people on FR have been unable to accept reality. You appear to be one of them.