Surely the Swiss and other financial tax havens like Luxembourg and Monaco would be more than happy to take London's business.
The fact is that the FVEYEs must be crippled financially so that they can no longer wage war against China.
China could and should use its financial muscle to encourage a mass migration of financial and other professionals services out of London. Or better still, use very thinly veiled threats of doing so as a means to put a leash on the British and rip them out of Five Eyes.
One of the key reasons that London was such a successful financial centre was because the UK was part of the EU. The EU is to Britain what China is to HK. Without the draw of the massive EU internal market, precisely what is the point of setting up shop in the UK?
The key advantage the UK offered was being an English speaking member of the EU, but they are not the only English speaking EU member. Ireland is right next door, and has a proven history of being very pro-Business (so much so the EU commission took them to court).
If China came knocking with an offer of the century to make Dublin the new London, or if they really want to stick the knife in, they can propose to make any of the secondary towns or cities on the Northern Ireland boarder the new Financial centre. That will then serve as a huge new source of wealth and employment, which the Irish government could easily make fully accessible to citizens from Northern Ireland, and I think you can see where this is going. Such a move will prompt a mass migration of financial and other professional services out of London to Ireland and Northern Ireland, while also massively strengthening the possibility of Irish reunification.