If WB wants to continue the DCEU largely intact, they'll continue with Cavill. A JL 2 is unlikely at this point, and would probably be a harder sell than a MOS 2. It would be very easy to sell a MOS 2 as a clean slate than getting new actors. Repeat recastings won't help the brand, unless they literally do a reboot of Superman the Movie. I just don't see that happening anytime soon. It's not that easy to find entirely new actors.
Look, I don't think Roven or Snyder or WB were ever planning to make a MOS 2 (there are a lot of little clues to this fact). However, Geoff Johns cares a great deal about Superman, and WB brought on Whedon in part to retool Cavill's Superman. And much of the negative discussion about the DCEU has focused on the problems with Superman (so there's some interest in the character still there). A MOS 2 might not be a certainty right now, but if the DCEU survives, and if WB ever hopes to make another JL film, they'll need to make a Superman sequel at some point.
Again, I guess the key is if they want to keep the shared universe going. My fear is that WB essentially abandons the shared universe idea (they were never fully on board with it) and splits up Aquaman, Shazam, WW, Batman and the other films. If that happens, then I would expect a Superman the Movie reboot (5-10 years down the line).