No problem. The same people arrive from even later in the future with enough built-in power for both machines and rescue themselves. Everyone returns to their own times. When they arrive back in the earlier time, now they know they have to build another machine with spare power to go rescue themselves.
What I love about that scene is that Bill and Ted are too dumb to know what a paradox is, and how dangerous that can be for a stable timeline. Instead, they just intuit the most useful way to abuse time travel and everything just happens to work out.
No problem. The same people arrive from even later in the future with enough built-in power for both machines and rescue themselves. Everyone returns to their own times. When they arrive back in the earlier time, now they know they have to build another machine with spare power to go rescue themselves.
trash can. remember a trash can.

What I love about that scene is that Bill and Ted are too dumb to know what a paradox is, and how dangerous that can be for a stable timeline. Instead, they just intuit the most useful way to abuse time travel and everything just happens to work out.
It’s the perfect culmination of how they solve all their problems: by being Bill and Ted!
I think my favorite example of this in the first film is when they unintentionally repeat So-crates’ philosophy back to him by quoting Kansas.