First, it's not possible for a hostile majority to fake transactions from another participant, because they still do not have that participant's private key(s).
Second, it's not possible for a hostile majority to force other nodes to forget a transaction that was seen, because once aby node has seen that transaction, it is free to remember it.
What a hostile majority of validator nodes can do is: (a) prevent certain transactions from entering the blockchain, i.e. being confirmed, and (b) retroactively change the consensus regarding the authoritative fork on the chain.
But one might say that, philosophically, if the majority of your validator nodes are hostile, then you probably have bigger problems than your blockchain consensus breaking down. It means that the majority of business relationships on which you were relying have broken down as well.