This is related to this question, but I'm curious about a slightly different angle.
Suppose someone makes a fanciful blessing. I'm not talking about, "May we be Zocheh to a Geulah Sheleimah BiMheirah," or "May the Neshamah have an 'Aliyah," because, despite the fact that these are outside the realm of our understanding, they are not outside the realm of possibility or what we believe must or can happen.
But what about, "May you know no more sorrow," or more fanciful ideas about a departed soul? Certainly life is full of moments of gladness and sorrow. If someone knows no sorrow in his life, then that likely means the person will predecease everyone that is related to him - that is not a blessing at all, and certainly the blessing is meant to imply that this person should live a life in which no circumstances of sadness should ever happen again. That is not something that can be reconciled with reality. I also recently saw something like, "May the Neshamah enjoy hearing the beautiful words read from the Torah written in their memory."
Should (or may) a person respond "Amen" to such a blessing/wish? Does this even count as such?