iPhone 7 display sealing adhesive is already available on Chinese sites. If you clean the old adhesive off using alcohol and apply the new one correctly, the screen will still be waterproof.
Can't say about the camera because it is sealed differently. If you push the camera internal bezel off, you will have a hard time locating new parts since they came welded onto the casing. The lens is glued onto the bezel, you have to make sure the bezel and the lens are also sealed.
After repairing everything, there is a simple method to test waterproofness. Tape over the speaker/vent grills on the bottom, take out the sim tray and try to suck air through it using a hand vacuum pump, if the pressure does not leak back into it slowly, it is sealed properly. You will have to find a way to connect the hose to the sim slot and seal it for the test though.