Unfortunately Gail, in most cases, yes, the complete window assembly will have to be removed, then disassembled in order to replace the broken glass in that lower section. But, it certainly isn’t a huge deal to remove and reinstall the window, but it will take two or three people depending on the size of the window.
Typically, the window sandwiches the wall between the outer frame and a piece of garnish trim around the perimeter, located inside the RV. In the photo, you can see the trim piece and the mounting screws. Begin by removing all the screws from around the garnish trim piece and place the trim aside. Next, carefully insert a wide blade putty knife under the exterior flange of the window to break the seal of the existing sealant. Have someone support the window from the outside as you gently push from the inside. At this point, all that is holding the window in place is the sealant around the perimeter of the exterior. Work the wide putty knife around the frame as you carefully push the window out of the opening through the sidewall.
Once removed, clean off all the remnants of butyl caulk or sealant from around the window flange and what may be left around the opening in the sidewall. Always use fresh new sealant when reinstalling the window. Once the window is out and cleaned off, it can be disassembled.
Depending on the brand of the window, somewhere around the perimeter of the frame, you should find a joining strip where the two ends of the formed frame come together. It is probably secured with rivets or screws. Either way, it will have to be taken apart in order to remove the rest of the broken glass. Or better yet, take the entire window assembly, in one piece, to the glass shop and have them do the disassembling and reassembling of the window itself. They’ll be able to seal the window properly within its frame also. You’ll only have to seal against leaks as you reinstall the window back into the RV. I recommend Eternabond double-stick tape when reinstalling the window into the motorhome. The Eternabond tape will help hold the window in place as you reinstall it, as well as seal it, but you should still have someone helping as you put it back in place.
From the outside, be sure there are no gaps anywhere around the perimeter of the window after all the screws through the garnish have been reinstalled. It may be necessary to install new screws, one size larger, if any appear to strip as you tighten them. Next, inspect the entire outside perimeter of the window. If any gaps exist between the window and the sidewall, water will have an entrance; and that is the biggest threat to guard against. In some cases, a double layer of sealing tape is required to ensure no gaps remain. If necessary, use a thin bead of silicone sealant along the top edge of the window just to be sure.
The bottom line is that you, most assuredly, do not want any water intrusion. It is also recommended to install new vinyl-backed foam tape on the inside flange of the garnish trim. It should also fully compress when you tighten the mounting screws, thereby effectuating a tight vapor seal. And that should do it! Keep in mind, if this appears too daunting for you, any number of local RV shops would be more than happy to perform the removal and reinstallation of the window for you.