In an ectopic pregnancy the child absolutely cannot survive to birth. If not aborted, the mother will also die.
Any reasonable person will concede that it is better to lose one life than two.
Thank you. Yes. I am not familiar with the intricacies of ectopic pregnancies, but am hesitant to accept the word “absolute” as applicable, if only because we may be able to make a way. Whatever we do, it is best to treat all human life with respect, and give the benefit of the doubt when uncertain.
I don't think the day is far off when a baby will be able to be saved in most cases of ectopic pregnancy, e.g. they could remove the fallopian tube; implant it, embryo and all, in the mother's uterus; then slit the tube open (imagine slitting a section of a drinking straw lengthwise) so placenta and baby have room to develop.
BTW, there have been (exceedingly rare) cases when a baby implanted ectopically on the mother's inner abdominal wall, and both survived. The baby had to be delivered surgically, of course.