Can Bitcoin continue as usual without a hard fork and without the core maintainers and their access to Bitcoin Core’s GitHub repository? A hard fork is out of the question since it will not be Bitcoin anymore.
Yes it could continue without core maintainers but like the name implies they are quite important in maintaining the bitcoin software and addressing bugs.
Not to mention it could lead to stagnation in its development.
Mind you there are other contributors that could help with development but won't be as efficient.
So the positions the current maintainers hold can be replaced. Found the names in an article from 2023 but it should be close to accurate if they didnt replace them recently.
Ford oversees the build system
Gloria Zhao writes and reviews the code that governs Bitcoin’s transaction validation process
Andrew Chow is in charge of programming for crypto wallets, which allow investors to store their bitcoin
Marco Falke focuses on testing
Stepanov maintains the network’s graphical user interface