Scott Weinberg of Minneapolis was out bicycling about three years ago when he had troubling thoughts: What if he got hit by a car? If so, what would happen to all of his social media accounts? So Weinberg saw a business opportunity. His online service, Protect Their Memories, is designed to help families in precisely that situation. When someone dies, the service helps survivors promptly wipe the deceased person’s accounts on Facebook, Twitter and six other top social networks.