While I realize that these days hay is like gold, I too would either return the bale (minus the dead body) to the vendor, or toss it. Actually, I don't really "toss" them - I either add them to my compost pile or spread them around my trees as mulch/fertilizer.
Believe it or not, I once found a whole dead rabbit inside a bale of hay, & when I next returned to my "former" hay/feed dealer & ask for a credit (the bale was a whole $5), they actually asked me to bring them the dead rabbit!!! Like I was lying awake at night thinking of ways to cheat them out of a $5 bale of hay that was part of a $300 load - lol!!!! I told them that I'd buried it in my compost pile & had no plans to dig it back up for verification. They did begrudgingly credit me the $5, & I switched hay vendors immediately thereafter. Geesh.
Depending on the size of the bale, I'd toss at least 2 flakes on either side.
With the way hay supplies are getting this year, I put out a round bale and decided to bite the bullet and do the botulism vaccines for my 2, especially since I have 2 other people feeding who just aren't as careful as I'd like. Since its their first time its a series of 3 boosters ($$$), but worth it.
Many years ago, one of out group noticed an Appaloosa gelding in the barn that was ignoring his dinner hay. Thinking he was colicky, I stepped into the stall to investigate. The horse seemed fine, but kept his back to the hay that had just been tossed on the floor. I went over, kicked the flakes to see if they were bad, and out popped the back half of a calf!
Needless to say, we removed that awful thing, all his hay, and replaced it with fresh hay.