The only way he’s not on the ballot is if the RNC refuses to accept him as their nominee..
If the RNC does this, the Republican party is DONE as a national party, at least 30% of their base, if not more will walk away from them and most of those that do will NEVER return.
How can the RNC refuse to recognize the nominee of their own convention? Assuming Trump has the delegates , how could this happen? Agreed it would be political suicide for the GOP to reject their own nominee, if somehow a coup was executed by Republican leaders.