So, is there a general lesson to be learned from this highly unusual lich encounter? In our case, we had a good idea of what we were up against, and we prepared extensively for it (which was how we ended up with 13 NPC allies, among other things). That preparation paid off, and we were able to go into the fight knowing the risks and ultimately emerge victorious (and we never had to use our emergency time reversal ability during the fight). Because we knew the risks going into it and we were the ones picking the fight, it never felt unfair that the lich had access to such powerful spells. In fact, the question of "fairness" never even came up. If we didn't feel confident that we could handle it, we would have avoided the fight and looked for another solution.