So, an update.
Turns out my dad didn't actually take the 16' Springbok out and search the lake for the boat (told me today he couldn't get the motor working)............. I'm not actually sure what he did, because OPP called and found the boat down on the south end of the lake hung up in some trees. Dock still attached and all. Looks like only some scratches to the boat and it didn't damage anyone else's property.
Thanks everyone for all the help and kind wishes while this was going on. Looks like Mother Nature was the culprit on this one.