I'm trying to get all historical rollbacks of Bitcoin and Ethereum. I get that there were hard-forks (e.g. DAO incident for Ethereum). How about rollbacks because of attack or miners failed to validate the block, etc.? Appreciate it if anyone knows or can point me to some external resources
Apart from Ethereum uncles and Bitcoin orphans which are tiny forks that happen all the time, these were two instances that I found related to bitcoin bugs:
https://en.bitcoin.it/wiki/Value_overflow_incident: rolled back by community patch https://en.bitcoin.it/wiki/DOS/STONED_incident: no rollback needed
To answer your question, the blockchain can never be rolled back due to failure of miners to validate a block. By definition, a block gets added once a miner validates a block. If all miners suddenly turned off their equipment, no blocks would be produced, and transactions would sit in mempool until some miner took advantage of the extremely low difficulty and started producing blocks again.