You can still imagine that as an end, and define an end based on that infinite stretch. At some point, you can't tell the difference between before and after more stretching, and you'll never be able to stretch in a way that can be noticed.

There's no more events to happen, and more so, no ability for more events to happen.

Thats still likely an artifact of our models though, and that when you do to something like that, that new events start happening again

If electrons decay, there will be a time when there's nothing in the universe which can function as a clock.

Which does not mean that time stops. If no one hears a tree fall that does not mean the tree isn't falling.

Not a physicist, but I know that there are physicists who disagree with that. See: Roger Penrose and CCC.

I'm not sure if Penrose suggests that time stops once there are only photons left. He says it is equivalent to the situation at the Big Bang and time certainly didn't stop there. In fact, in his conformal cyclical cosmology spacetime goes on indefinitely but just reboots regularily.

Right,but I think the idea implies that time is different, not that it keeps going on as normal. Honestly not sure though.

Apparently time requires mass...

Has it been proven that electrons decay?

I don't think so