Can’t say for sure, but they have figured how to make an exposed charge port safe to dunk I’m water. I am sure there will be some way to have both an enclosed battery and the terminals to connect the battery do the same. The phone may get larger to accommodate making this possible though, for anyone who remembers how chunky early 2000 replaceable batteries could be, I’m sure replaceable batteries will have to be something akin to that (though hopefully a little more streamlined)

Samsung did it with the Galaxy S6, so it’s definitely possible to do; just not as profitable. Hopefully the EU will force these companies to make something slightly less profitable but much more usable long term