If a changed organism does not successfully pass on it’s genes, it is just a dead end, evolutionarily speaking.
You could have mutations that survive to reproduction. You could also have a hybrid (a virtually new cross breed creature) that survives to reproduction (although a lot of hybrids cannot reproduce).
As environmental contingencies change, the characteristics that have helped an organism survive to reproduction, may also change. Hence some organisms’ species can become extinct with the drastic changing of the environmental contingencies. And new, or at least, altered species would be expected to arise.