I read a bit more on what Amendment 25 can actually do with a President who isn't in a coma, and it looks like it is only effective for about four days unless Congress is dead set on extending it. So Amendment 25 takes him out immediately as impeachment works it's way through the process.

One interesting thing is that as acting President, Pence would not be able to pardon anybody (because Trump would still be President, just stripped of his powers). Once impeachment and removal was complete, Pence WOULD be President with the power to pardon for federal crimes. I wonder if that might be incentive for impeachment for somebody, either in executive positions or Congress. But maybe that's giving too much credit to those people.