Host machine power-off while merging due to delete snaphot

[accord]

I started to delete a snapshot that I need by accident and VirtualBox started merging, so decided to power-off my machine (my host, by holding the power button down for 4 secs).
Will it cause any damage to my snapshots?
My theory is that the merge hopefully done to a temporary file first. Is that true?
Are there any verify mechanism against damaged snapshots? (i.e. CRC)
It seems my snapshots are working but I don't know if there is any subtle problem which may emerge at some point.
My backup is VERY old