Perhaps, We can breakdown The Bracha L’vatala into two dinim.
1. When making a Bracha L., you are oiver an Issur. ( Lo Sisa Shaim-)
2. The Bracha you made, is an invalid Bracha.
If some one makes a Bracha “ Al Achilas Matza” and is Motzie
others with his Bracha , but he drops dead before he eats the Matzah,
It is possible, that the others have to make a new Bracha before eating
their Matzah. They were not Yotze with the Bracha,the
dead man made , being the Bracha was a Bracha L. (#2 invalid Bracha)
Even though the dead man wasn’t oiver the Issur (not his fault that he died),
but it is still considered an invalid Bracha.
The same would apply to someone who made a Bracha “Al Sefiras Haomer”
and drops dead before counting, his Bracha is L’vatala and not considered
a valid Bracha.
According to the Poskim who hold, " not finishing the 49 days (one Mitzvah)
the Brachos he made in the past are L’vatala", the same would apply to someone
who dies during Sefira. His Brachos are considered L’vatala, only to invalidate
them but not to be oiver on the Issur.