Grim reapers are supposed to close after they exit. It is the way theyre designed. It is dang near impossible from them to fail. Just google grim reaper failures. Most of the "failures" ending up being shot placement. I'm not saying you made a bad shot, but until you find the deer we can't say for sure.
As for fixed vs mechanical, the only reason to shoot mechanical is accuracy. Any time you put wings on something you give it the ability to steer itself. The fixed blades would act as wings. As for mechanicals, anything mechanical can fail. Thats why I shoot the ones with the smallest failure rate. That's why I shot grim reaper.
Hope you find your deer.
