Even Mormons?
Ah... that's a tricky one. That (along with everything else) is up to God. I'll tell them I believe they are wrong, just as I'll tell you I believe you are wrong; but I'm not their judge... I'm not even on the jury.
I believe the Catholic Church is the ordinary vehicle of Salvation because I believe Our Lord ordained it so. I am fearful for all outside of her but not totally without hope. If one is truly attached to Christ then in some way there must be an attachment to His Church, even if it's unknown.