If you want to look at it from such a fundamentalist angle, sure, animal testing is immortal. You'd only be able to test new drugs on terminally ill patients then.

If you're willing to humor me, let me take you on a tanget. I promise it'll make sense: Do you agree that CO2 emissions are fundamentally wrong (leading to a mass extinction event, etc)?

(I will continue this argument under the assumption that we can all agree on that) And do you concede that these emissions are, for the foreseeable decade(s) inseparable from modern human life? Not that they are a basic necessity to survive, but that you and I are indirectly causing such emissions in one way or another for every day that we are alive and continue with our day to day actions (heating, cooking, buying stuff, transportation, etc). This may change in the future, but let's focus on today.

(Again I assume that you are not the 0.1% of the population that lives without any modern amenities (you have some way of writing comments on the Internet for example), and will continue my argument) Given these two basic building blocks of our mutual understanding of the world:
Neither you nor me have committed suicide. So there is a reason that we continue on living, despite our continued existence being linked to habitat destruction and animal deaths. We are working towards a better future and try to change that, but for some reason we consider our current lives more important than the lives of animals that are threatened as a consequence of our existence. I don't know why, and you probably neither. I guess it's just some deeply rooted desire for survival.

Oh, btw, I am actually curious what your answer is to the 100 rats question someone else posted in the comments. Or maybe rephrased a bit: is there any number of rats (or rabbits or fish or dogs) whose deaths you're unwilling to accept and that makes you say "no, take my sibling/partner/parents instead"?