and the evidence remains in the blockchain making liability easily provable.... that evidence filled blockchain is likely to be deleted when the witnesses move on.
But...
The blockchain is a public ledger system which is currently not deleted and easily copied for any purpose whatsoever including future legal actions.
So, purposeful deletion of the blockchain is unlikely to result in complete deletion of any such evidence. No one can be quite sure that there aren't multiple copies being made every few days.
This is very true, and entirely possible, and I actually think there are folks undertaking to do so.
I hope they succeed, without reservation whatsoever.
If they're not, there must be reasons for it. For myself, I reckon I have no cause of action, and neither any capacity to undertake such expense in time and treasure.