“but according to a senior Republican National Committee official that does not mean he will become the GOP presidential nominee.”
It will be then end of the Republican Party as we know it then.
The primaries that have brought a Liberal Democrat (of the older Harry Truman, Sam Nunn, sort) to the cusp of being the Republican nominee has already accomplished that. The only question is whether this new populist version of the party will win in November or effectively split into two and put Hillary Clinton into the White House. But the deed which starts it all is done.