I am so sorry for your loss, a terrible thing to happen to a beloved pet.
On the surviving ducks: Animals are much more resilient than we humans. A temporary change in their location (your garage) could be all that is necessary to give them time to get back to their normal routine. I would leave them in the garage area for a week or two, then take them back to their normal home and see what happens. By then you will have had plenty of time to remove all old bedding, clean all surfaces with a 10:1 water/bleach solution (rinsing well), let it air out and air dry, and replace with fresh new bedding. This will also give you some time to make any predator proof modifications to their entire enclosure.
On predator proofing: You can make a completely "fenced in" enclosure for the ducks, complete with aviary netting and create a predator proof environment. It is very costly. We have done this for our chickens and our ducks are currently housed with them. If this is the route you decide to go let me give you a few words of advice: We used 4 X 4 treated posts and then connected them with 2 X 4 treated lumber a quarter inch above ground level, half-way up the middle and then again across the top, so it's like a 3 rail fence. On the bottom section we used 1/4 inch hardware cloth, this prevent any little hands (raccoon, mink, etc.) from reaching in and grabbing dinner(which they WILL DO if you use anything larger). On the top half we used 1 inch chicken wire, this allows flying bugs to still get in the enclosure, across the top we have aviary netting, this prevents the resident hawk from gaining access from the sky. On the outside along the fence line (on the ground) we place 12 inch X 12 inch concrete pavers, these are way too heavy for any form of wildlife to pick up and move. Internet advice says to bury your wire two feet underground, however we did this before and had stray dogs dig under and gain access to our birds, concrete pavers have done the trick for 3 years now and nothing has been able to dig under.
If you decide you would rather not go to this extreme consider this: If your "sleeping enclosure" has a wooden floor, put a "door" on the front that you can close and lock up after the ducks have gone to bed. Having a wood floor protects them from anything trying to dig under the structure, it can dig all it wants but never get through the wood floor. Having a door that you can close up and lock means nothing can "get in and at them" after you have put them to bed at night. Of course this also means that you have an added responsibility of letting them out in the morning and putting them to bed at night.
On wildlife in general: There are livestock/pet owners that look at wildlife and say, hey, they're hungry, they're just looking for a meal, we are encroaching on their territory, etc. I get that, I understand and to a certain extent I agree. It is definitely a dilemma. Two years ago we "live trapped" 6 (yes six!) raccoons in our vegetable garden in 2 months! Relocated those puppies 50 miles from our home (husband dropped them off at the river bottom on his way to work). Two weekends ago we had to shoot one in our yard at 1:30 in the afternoon. We live in Texas which is under a rabies state health emergency, so when you see a raccoon in the middle of the afternoon you dispatch the thing to protect yourself, your own livestock, your neighbors, their livestock and every bodies pets in between. To Mr. Raccoon I say, "Go hunt and eat Mr. Squirrel who also likes to eat my tomatoes and leave my chickens and ducks alone (or else)."
