Saying "X has a right to live" means "you shouldn't kill X." That's a completely different statement from "you will not be able to kill X."
Morality is concerned with what you are obligated to do or not do, apart from your preferences or abilities.
This has been hashed out before. Doesn't go well for "rights" in the sense you mean.
Furthermore, you could've made the same comment about us [humans] just a few thousand years ago. And considering the rate of evolution compared to the length of time this planet is going to be around for, it's probably a bad idea to extrapolate the fate of dolphins in the future based on their current capabilities.
This wasn't always the case, and may not be true in a million years.
There is nothing stopping you...just keep walking west. :)
Someone that is brain-dead can't self-sustain, are there no legal/ethical qualms if I pull the plug?
Are disabled people open season for abuse because they are 'lesser' than the rest of us?