Will the file be corrupted and unable to fix (i.e. none of any data can be recovered?)
Potentially, yes. There's 2 obvious routes via which this could happen.
Ext4 is a metadata journaling filesystem - it only journals the changes to the file's meta data (size, location, dates) - not the file contents (btrfs and zfs do full-data journalling at a big performance cost). So although you should never have to fsck the disk, it doesn't follow that every write operation betwen opening the file and closing + flushing the buffers will have completed. There is no transactional control over writes to the file data.
A second possibility is that the disk may be physically damaged by power spikes. Although the rest of the hardware tends to do a good job of isolating the hard disk, there will still be some leakage.
will there be a chance the file system be completely unable to boot?
That's a very different question - this is a lot less likely. Certainly the first scenario only applies if you happen to be writing the kernel, bootloader, ramdisk etc at the time of the outage.
See also this Q&A on unix.stackexchange