>is it possible that due to OS crash or mysql itself crash or some e.g.
>SCSI failure to lose all the data stored in the table (let's say million
>of 1KB rows).

It is always possible that your computer system will catch fire and
lose all data EVEN IF IT'S POWERED OFF. And the same nuclear attack
might take up all your backups, too. And you and all your employees.
Or the whole thing could just be stolen.

Managing to smash just one sector, the sector containing the data
file inode, or worse, the sector containing the data file, index
file, AND table definition inodes, could pretty well kill a table.
I have had the experience of a hard disk controller that sometimes
flipped some bits in the sectors before writing them. It took weeks
to discover this.

>In other words what is the worst case scenario for MyISAM
>backend?

Probably, total loss of data and hardware.

>Also is it possible to not to lose data but get them corrupted?

I call that 'lost'. But yes, it is possible to end up with a bunch
of data that's bad and you don't realize it until things have gotten
much worse.