There is no obligation to sign out at the end of a trip. I also don't know how regularly they check dashboards for permits. That could vary by access point. So, the park won't necessarily know if you are overdue. I think the most reliable trigger for a search is if someone or some service calls.
Otherwise, they may track certain permits during particularly hazardous weather events. I'm linking to a story over on CCR where a late season solo traveller was a day overdue. The weather had turned bad and the Park and OPP had invloved helicopters, ambulances, boats and a full blown search and resuce command post. This is not a regular procedure. I think it has more to do with the weather and time of year. The solo tripper was fine, just a day behind.
http://www.myccr.com/phpbbforum/viewtopic.php?f=108&t=31416
On all trips I make a float plan that I leave at home with my family. It details trip particulars, when I am supposed to be back, my planned route, and who to contact in case of emergency. I also carry a spot that I use to send out one of 4 messages: I'm OK; I've been delayed; This is not a life threatening emergency but I need help, call ###-####; and of course 911.
To show you the sort info I include on my float plan here is a screen grab.
