I think mechanical reliability of most modern bikes is a given and your chances of a triumph-specific failure on a road trip are miniscule. I certainly don't look into dealer locations when I'm travelling any more than I would for my car.
That said, parts stockage is a potential issue. I think it's pretty routine for even large dealers to have to get stuff from england. I'm not sure how different another brand or even a modern car would be if (say) some EFI widget burned out.
Like I say, I don't worry about it but it is a potential issue.
Oh, a last cheery thought: a breakdown seems unlikely but a minor accident does not. I believe Wild Mike got hung up chasing parts in Canada when he took out one of our deer - serves him right!
