Yes that would make sense tab. I think for me a decision to give birth at term would be easier knowing a baby was likely to die, rather than be seriously ill for many years. The problem of course is that that is so hard to predict. I have met children with dire predictions about their hearts made from scans in pregnancy who have been born, needed a couple of ops that were not as major as suggested during pregnancy and then been absolutely fine. Of course there will be others without that outcome.
The other possibility I guess is that an in utero death might have been damaging for the other twin. But that's all guess work. People have the choice with disability to terminate to term and I don't suppose the presence of another baby affects that (indeed would make it harder to deal with a seriously ill child).