The best answer right now is that we just don’t know and that in part is because DC doesn’t seem to know.
The critical and financial failures of the justice league and Batman vs Superman films made Warner Brothers rethink there plans and from what we can tell success of wonder woman, Aquaman and Shazam has led to them focusing on standalone movies rather then forcing crossovers on the public.
Currently the release plans are Birds of Prey and Wonder Woman 2 in 2020 there are no indicators of any crossover here.
2021 the Batman, suicide squad (confirmed reboot/re imagining), and black Adam.
Shazam 2, Aquaman 2 and the flash in 2022.
Given black Adam and Shazam have history there is a possibility for crossover with these films but it seems that Warner is doing a soft reboot, accepting the events of justice league happened but not directly continuing on those story arcs. Shazam at least confirmed there is a Batman and Superman in the dceu they may take a bold option and just change actor as marvel did with the hulk in the mcu, without rebooting the character.
The flash is not being recast nor are Shazam and wonder woman, as far as I am aware Dwayne Johnson is still plying black Adam so the dceu is certainly not being canceled, to date it has made just over 5 billion in revenue and Aquaman broke 1 billion so they have seen that when done right the franchise with these actors is worth money.
Crisis on infinite earths showed that the tv dceu does exist in parallel to the movie universe (grant gustin’s flash met Ezra Miller). So if any of the movie actors start to struggle they could slip through a crack in the universe to a successfully well written dc franchise easily ;).
In addition we have to coinsider the newly created Teen Titan's and Doom Patrol series, both of which I believe are meant to fit in the DCEU as opposed to the Arrow Verse in much the same way as Marvels TV shows are meant to compliment the wider MCU
