Since my needs aren't mission-critical, I can afford to lose some data. But would the rest of the data on the HD be corrupted?
Enable filesystem barriers on all you're mounts, if you can afford to lose some data the maximum loss in this scenario would be your cache size, but on average it should be quite a bit less.
Note that barriers reduce I/O performance but improve the integrity of you're filesystem greatly -- especially when using disks that attempt to re-order writes.
man 8 mount
barrier=0 / barrier=1 / barrier / nobarrier
This enables/disables the use of write barriers in the jbd code.
barrier=0 disables, barrier=1 enables. This also requires an IO
stack which can support barriers, and if jbd gets an error on a
barrier write, it will disable again with a warning. Write bar‐
riers enforce proper on-disk ordering of journal commits, making
volatile disk write caches safe to use, at some performance
penalty. If your disks are battery-backed in one way or
another, disabling barriers may safely improve performance. The
mount options "barrier" and "nobarrier" can also be used to
enable or disable barriers, for consistency with other ext4
The ext4 filesystem enables write barriers by default.
Theoretically, the journal would save you from filesystem corruption due to a sudden loss of power because metadata will be guaranteed to be well-ordered.