My betta never bothered adult shrimp for the years that I had him. Unfortunately when I went on vacation my friend over fed him too the point that when i got home after 4 days the entire tank was foggy and there was hundreds of pellets on the bottom of the tank. A few days later he had some bad infection and died. I told them to give him 3 pellets a day! Anyways, usually I find shrimp carcasses when they pass. Some of them will be ate but I have found one from time to time. Most were old age i think as my first batch was probably 3 years ago. A shrimp carcass, no matter what color they are alive, is a white/pinkish. It is easily recognizable from a molting shell. As far as I have found, most fish just leave the shrimp alone. I have glowlight and rummy nose tetras, as well as white cloud minnows, 3 large yo yo loaches, a cuckoo catfish and some dwarf frogs. Not even the loaches bother the shrimp. The ghost shrimp and cherries seem to be self sustaining but I imagine most of the hatchlings/ smallest of babies that get too brave and venture out of the floating hornwort clump get ate.
Furthermore, shrimp are great hiders. I remember when i first added them to my tank, I got 10 at the pet store. The next morning I could not find them ANYWHERE. I was so upset that I was about the tear down the tank and get rid of the yo yo loaches. The next morning when i went to feed the fish i counted 8 cherry shrimp and they were all fine and happy. I am sure the other two were just hiding somewhere as well. Especially after a water change, you can expect them to molt and hide for a few days as their new shells get nice and hard.