While a complete reboot would probably be the simplest route, I'm cool with Cavill possibly coming back. Maybe I'm biased because he was my choice for the role going back to the Flyby days, but I've enjoyed him in the role despite the movies him appearing in having serious flaws.
Please God, no. I've had enough with reboot talk. They have their expanded universe, save trying to recreate it, they just need to fix what they've got.
It's been said already, but they've got solid performances out of Jason, Gal and Zack (Levi) who are undoubtedly still on board for future films, and Cavil is still interested in portraying Superman. You've got four members of the Justice League nailed down, be that independent films or not.
I don't know if they're going to have Patterson's Batman enter the fray here, but that can be done via time travel shenanigans if they really wanted too - although I suspect that his Batman would be a self contained trilogy, much alike Phoenix's Joker film. I can't even think what they're going to do with Batfleck, short of an actual recast. Successful or not, I don't see Affleck returning after the Snyder cut, not unless he signs a deal similar to Cavil and comes in more as a cameo/supporting role, but they're going to need an actual Batman for an eventual JL sequel, and I doubt very much that Ben is on for that, unfortunately.
WW84, the Suicide Squad sequel, Patterson's Batman, Black Adam, the Flash, Shazam 2 and Aquaman 2 are the next films to be released, and in that order, although one does wonder whether the Flash will be postponed (again). I know also that there's a bunch of other projects in early development, but honestly, WB should be looking to get a Green Lantern Corps going before anything else. Whether it's within the next five years or longer, a Justice League sequel is going to need an active member of the Lantern Corps, among other characters (such as Hawkgirl, and maybe Martian Manhunter if the Snyder Cut allows for that transition).