Our HR Vacationer has this same type of awning over the slides. We just spent this past weekend in North Cove Washington (just south of Westport), experiencing one of the heaviest rainstorms we have been camping in. While our awnings continued to collect and run-off the rainwater, I am certain that there was some collection of water up there.
We left our slides out the entire weekend and did not experience a single problem with water getting inside nor with the awnings remaining out. Granted, we did not pull them fully out (which acts as a shade over the window when fully extended) but survived this storm fine.
I had my wife retract the slides as I watched them from the outside of the coach, and had her step them in a little at a time. Figured that would allow any trapped rainwater to run off the awning, making sure none of it found its way to the top of the slide as it was coming in. We did have some snow make its way in this past winter, managed to get blown in beneath the awning and melted once the slide was retracted. Made a bit of a mess although nothing was damaged.
If I was concerned about the duration of the water remaining puddled up, I would suck in the slide and dump the water off the awning as it rolls itself up.
Good luck and happy trails.