I suspect when everybody knows he's lost, he will have a psychotic break and be drugged into docility. He'll probably be shipped off to some very private sanitarium "to recover from a health problem". I just can't see him taking part in a transition of power. Maybe Pence even gets put in command. There are just too many people in the Secret Service who want the US to remain a Constitutional Republic instead of a South American Dictatorship. Trump may have his fans there, but mostly these are educated professionals sworn to uphold the Constitution. No Governor will claim his state's voting was rigged, mainly because the Republican Governors are from Red states where Trump is likely to win! They might claim some other state's voting was rigged, but they have no power to affect the process in other states.

Voting in America is actually very transparent: You can count the precinct tallies and see that they add up to the state totals. States have their own rules about winner-take-all or proportionate electoral votes, and those would have to have been changed by the state assembly long ago.

If you want to rig elections it's way easier to manipulate voters' opinions, and suppress voting.