Terri will die because she had a fatal arrhythmia 15 years ago, possibly brought on by bulimia. Instead of dying then she was miraculously kept alive while her brain, severely deprived of oxygen at the initial event, continued to atrophy. There is now 20% of the cortex left. Terri will die because modern medical science is no longer keeping her alive via a feeding tube, inserted surgically, and because antibiotics administered for every UTI caused by the catheter in her bladder or every wound infection from the feeding tube have prevented nature from running its course.
Terri will die because our advanced technology has forced us to write laws that will allow people to decline that the shell of their body be kept breathing and their heart beating with no remaining intelligence or any brain activity otherwise that would identify her as human versus the instincts of an invertebrate.
Cruelly put perhaps, but true.
Terri Schiavo has better brain function than some of the posters here coolly cheering on her death. Certainly she has better spiritual function and health.