I'm pretty sure stellar uses more or less the same consensus mechanism as the XRPL and there is absolutely no way to reverse transactions. Every few seconds a ledger is closed and it can not be changed anymore. If all validators would agree on one Tx being "bad" they would need to exclude it from the very first moment and from that point on to eternity. There would be a valid signed public Tx that isn't processes. So it would be public know that the system is corrupt. People who disagree with that could fork include the Tx and move on. This is a totally different kind of risk than if Tx can actually be reversed.