I think that concerns about this being the end of Arm are overdone - I expect that the UK government will get some assurances about maintaining the HQ in the UK etc and that Arm's business is sufficiently different to Nvidia's to make wholesale merger with Nvidia's existing operations counterproductive.

However, I can't see how they will avoid enormous conflicts of interest between Nvidia and other competing Arm customers and that this will be to the detriment of everyone who makes and uses Arm based products (except Nvidia).