It's easy enough to fall into the water while in the dinghy. I've done it a couple of times myself. Forget about smimming to shore - get back aboard the dinghy, even if it has been capsized, or the big boat QUICK. You should know how to get aboard your dinghy from the water (often easier said than done so that's why you should try in controlled conditions in warm water) and have a way to go aboard the big boat quick. Obviously, some boats (like those with sugar scoops) are better than others but any boat can be retrofitted with some (preferably, foolproof) way of getting aboard. My boat, for instance, has steps welded onto the transom. Other ways are possible. The point is to give some sober thought to this possibility and have a realistic plan in place.
I don't think enough sailors appreciate how easy it is to DIE in your dinghy. There are a lot of things you can do to prevent this from happening, including having a bag filled with emergency gear, a dinghy anchor, and REAL oars.
Jerry