Nvidia will certainly try to get as much money out of ARM's R&D capabilities, existing IP, and future roadmap as they can. They will get their money's worth - at worst they will fail trying. In that sense, they won't destroy "ARM the company" or "ARM the IP". But Nvidia will have no interest in maintaining ARM's business model whereby ARM fosters a community of Nvidia competitors - they have an interest to the opposite. Therefore they very likely will destroy "ARM the ecosystem".
It’s not going to destroy the business it’s going to destroy the current business model. The point is that the only way this deal can make sense for Nvidia, is to use ARM’s IP as a competitive advantage over other competitors. Until now, ARM’s value proposition has been IP neutrality for the various user companies.
But why would a company spend that much money to buy a company and destroy it afterwards?