The solana docs recommend using the "confirmed" commitment level for processing series of dependent transactions, but details are scarce on the probability of rollback after a transaction reaches the confirmed state.
Are there any stats available about the likelihood of a transaction being rolled back after it reaches a confirmed commitment?
A "confirmed" block is one that has received votes from 2/3s of the stake on the cluster. A "finalized" block is one that has had 31+ more confirmed blocks built on top of it.
As Jon's answer mentions, there has never been an instance of a confirmed block getting rolled back. Whenever the validators are forced to do a network restart, they always restart from the last confirmed block.
To answer your question more directly, I believe the only situation in which a confirmed block could be rolled back is if the network operators all socially agree to restart the network from a block prior to the latest confirmed one.
As of this writing, a "confirmed" block has never been rolled back.
