Any failure in your RAM pretty much fucks up your computer. Luckily, it's rare for RAM to fail after it's properly installed.
Yeah, that's why mission critical configurations have ECC and not for normal consumers. Even a slight corruption in the chainstate would be bad.
Each time Bitcoin Core verifies a block, it reads/writes a lot to chainstate. If you're low on RAM, the disk will be the bottleneck.
Bitcoin Core only stores as much chainstate on the ram as you allow it. Keeping the entire chainstate on the RAM, permanently and not as a cache, would probably cause more problems than it solves.
Regardless, the behavior for the chainstate flushing during IBD of a pruned node should be that the flushing occurs everytime that the blocks are removed from disk. Even if RAM is extremely reliable and that the server is never shutdown, Core would still attempt to flush chainstate to disk as the IBD progresses. Hence, it is necessary for the disk to have sufficient space to accomodate the chainstate, no way around that.