The Shimano pins have little barbed ends which go through and lock into place. Your repair depends of friction alone, which isn't really enough when there's virtually zero overhang on the end of the plate.

Whether the chain holds up or not depends on your riding and shifting habits. Modern index shift systems allow shifting under load but it causes tremendous side pressure on the outer plates, thus the peened rivets. If you don't shift under load, you don't create the side stress and aren't as dependent on the peened rivets to keep the plates from coming off the ends.

Some people splice chains and ride for thousands of miles without problems, others break the chain within a few miles. If you decide to keep riding, or can't find the repaired link, cut a square notch out of a dead credit card and carefully file it open until the outer plates can just barely pass. From time to time, run your chain through this gauge and if a plat is spread it'll snag and you'll know not to ride the chain any longer, and which bad splice needs to be cut out an replaced.