"is there any possible way to not get randomly nuked by Spamhaus?"

I guess the first step is to set up better monitoring services to prevent your system from being abused by even one bad apple. Try to catch the abuse as quick as possible so you won't raise red flags.

Additionally you should possibly work on segmenting out your customers. If your paying customers are important to you, use a different system for them. If this has the possibility of happening again you don't want to hurt those customers from a similar thing happening again.