-1. I've seen many terrible rules and rule suggestions on DarkRP in my time playing Garry's Mod, and this has to be one of them. The amount of servers that make it FailRP to destroy printers or other valuables while you're being raided or about to be raided is actually quite high and it upsets me. No offense to you, it is a completely understandable situation that you're explaining but there just isn't a point in adding such a rule. It restricts the player's ability to roleplay. I could care less if I raided a base and the printers got destroyed. I'd wait and try again later because after all it is a game and that is possible. Printers and printer upgrades get quite expensive and if someone wants to make the decision of destroying and re-purchasing/upgrading a printer rather than just losing their printer for someone to sell it back or something then oh well, that is completely on them and should have nothing to do with staff.
There are also other things to consider: what happens if somebody unrelated to the base or raid destroys the printer(s)? How do you prove that the owner of the base did or didn't do it? What if the raider does it and then proceeds to report the raid defenders, but no evidence supports the defenders being innocent? What if a printer is accidentally destroyed during a raid by a defender (ricochet, shot through prop)? It in short isn't a simple rule addition if it were even possible to be added.