Are all Summoning animals Immortal in a sense
The summoned animals live for a long period of time with respect to the human world, but that amount of lifespan is usual in their world (like toads in Mount Myoboku).


  Mount Myōboku has records of its population in a list, and the name of a Mount Myōboku toad stays there until it dies.[7]


I found the above in the wiki page of Mount Myoboku. So its safe to assume that toads do die and are not immortal. They just live very long.