Nothing. It will be a huge burden for them to maintain all the removed code. Their only choice is to integrate brave's adblocker.

This seems to be the only way forward from what I can figure. Helium's main selling point is that it's essentially degoogled chromium + a few miscellaneous patches & full uBlock. But once Google completely strips all that out of Chromium project, that won't be a tenable option.

I'm not sure what Opera/Vivaldi/et al. use for their native adblocking, but Brave's rust adblocker makes the most sense to me. Really it's uBlock's filtering lists that keep the whole thing working anyway.