It seems to me that Cruz is making a bet that a lot of the Trump primary supporters will simply not show up to vote in the primaries in 2020 and it will be a more normal process. Trump did bring in a lot of voters who were general election Republican voters (including many R leaning indies) but tended not to vote in primaries. Cruz wants a do over and go back to his plan of dominating with the evangelicals and riding them to victory with early wins in IA and SC and then sweeping the south on Super Tuesday.
It is noteworthy that one of the things his delegates were pushing for at the RNC was to get all GOP primaries and caucuses closed. They failed in that effort but that didn't change his speech. He just better hope those Trump primary voters don't show up or have a short memory.
And in fact, Cruz probably missed his golden opportunity. He could have traded his endorsement of Trump for Trump's agreement to close the primaries, sit pretty and win, whatever happens in November
Cruz doesn't have the social skills necessary to forge such an agreement.