Who has placed this rule on the property? Your lender? I don't know how they could enforce this, or even how they would discover this unless you defaulted on the loan.
Unlike other posters, I would not suggest that you talk with your lender - if there is a way for them to enforce it, you're the one raising the issue. They may tell you that you have to give them their money back! (I don't really think that they will, but who knows?) Instead, you may wish to seek legal advice if you're concerned.
HOWEVER, I will tell you that *generally* speaking, statements to that effect have to do with intentions...just as another prior poster indicated. Having a mom who had a stroke several years ago (and then she needed to move in with me) I know that things that you didn't expect do happen... and there's simply nothing you can do. I can't imagine that a lender wouldn't acknowledge that, and would be able to force you to continue to live in the home if your family obligations made that impractical.