You can run multiple clients, sure. I do it when running GG and having my alt on follow, I (and many others) have crystal farmer alt parked at a tower. You are supposed to do it on one box, not on several - see
Proof of Magic thread which had interesting discussion on it.
But, they don't do anything as involved as active SW participation. They collect merits from towers or from balloons shot by flame towers. I switch to them once in while to check on them or participate in tower defense, then go back to main. There is no way to script that much that they could be useful in battle. At best, you can have pocket healer on follow; and anyone who has toon on follow can tell you how unreliable follow really is.
And they don't disconnect at same time either. There are cases when more than one toon disconnects, sure, most of them have to do with massive attacks on heavily flame tower fortified locations. Dozen of flames and dozen of toons at same spot tends to create chaos and it could cause 2 maybe 3 disconnects in a row during assault. Nothing on the scale Zid saw and nothing that would crash the same person. Disconnects are ROM client specific, not box specific or user specific.