Brassard stated that dilation was necessary for the first six months to prevent health complications (infection is the only one I recall), but that after that, ceasing dilation would simply risk the loss of the cavity.
Personally, I dilate once every few months and haven't lost depth or width, so I also wouldn't assume that not dilating means the vagina will close up - so if you were *hoping* that it would be possible to cause the vagina to close up, that isn't guaranteed. Sometimes it does, but sometimes lack of dilation has no real consequences, particularly for very long-term post-ops. (This is not the same thing as advising that anyone do anything against their surgeon's recommendations, of course.)