I don't think so. I believe this makes the assumption that no matter what, with a POD in 1898 or in 1945 China will eventually become a superpower or that Britain will definitely lose its superpower status, and I don't think that you can make those assumptions.
It makes neither assumption.
It does make the assumption that some form of Chinese nationalism will continue to entrench itself and that there will be some form of Chinese state; but while the way that nationalism asserts itself might well change dramatically, I don't think anyone here would suggest that by 1898 it will be rolled back.
The assumption that there will be some form of Chinese state is also hard to fault; it could be that Britain holds onto Hong Kong if China disintegrates into nuclear fire, but that's a rather different timeline and genre. There may be no Chinese state if China is entirely partitioned; however, that in turn requires us not only to believe that colonialism will not just last but grow stronger when by the putative POD the killing flaws of empire all existed but that Britain will overturn a century's worth of strategy and suddenly decide to carve up China rather than back a central government.
To begin with, ignore any idea that the city can be held by force.
You correctly note that 1898 is the crucial year- the New Territories being leased, not ceded, means that British Hong Kong is on a countdown clock. The city simply cannot be held without the New Territories- it's where the power, the water and the people are.
However, even if we assume that for whatever reason the British ask for a permanent cession (I'm not aware that they ever considered this,) and that the Qing will grant it (by no means to be assumed, but that's another story,) the New Territories cannot be defended.
I don't mean against a Great Power: I mean that the British could not have stopped the Nanking Government from taking the city, any more than they could have stopped the PRC in the sixties. They probably could not have stopped at least some of the more formidable warlord armies. Any vaguely modern force can bring more men and equipment to bear than Britain can possibly station in the city.
That means that in 1997 the city must be defended with nuclear weapons. I find it very hard to imagine that a Britain that is even nominally democratic will be able to justify starting a nuclear war to keep a Chinese city- acquired in what is popularly regarded as one of the most notorious acts of imperialism of the nineteenth century- from being part of China.
Let's move on to the bigger point though, that there's no indication of why any British government would want to fight.
The problem comes down to what Hong Kong is for: its strategic use as a base for the Royal Navy was never as important as its role as an entrepôt.
Hong Kong isn't the prize.
China is the prize.
The city exists to be a foothold in the Chinese market.
So let's run through some scenarios.
Worst Case:
The government that wants Hong Kong in 1997 is hostile to Britain. It also denies Britain any role in the Chinese economy.
British options: Nuclear warfare in the service of a territory that, in this scenario, has no useful purpose to Britain and frankly has very few white people... or handing it over. It'll hand it over.
Historic
The government that wants Hong Kong in 1997 is ambivalent about Britain diplomatically, but bang in favor of British money.
British options: Are you kidding? The only question was what fig leaves they could get to make it seem like they haven't sold out the residents- but seriously, had you seen the projections for China's economic growth? Something something end of history. It was handed over.
Milk and Puppies scenario
The government that wants Hong Kong is a Friendly Capitalist Democracy.
Obviously it gets handed over.
Fragile Democracy:
Somehow, the PRC fell apart in 1989. Or the Nanking government has staggered on for a few decades. The point is that this is not a strong China. It is fragile internally, and its armed forces are- somehow- in such disarray that they couldn't take the city.
British options: Keep the city, and do serious harm to the government and market that is worth far more politically or economically than Hong Kong, or hand it over. It'll be handed over.
Chinese strength isn't that relevant, since functionally speaking the Chinese state would have to be almost non-existent to be in a position where the city can be held.
British strength isn't that relevant. Even a superpower can't station enough troops to resist an incursion with anything other than nuclear force.
What matters is what Britain gains from Hong Kong, and by the middle to late twentieth century it gains very little from keeping it in the face of Chinese opposition.
But what if the British Hong Kongers demand the protection of their democratic rights?
They'll be sold out.
Evidence: There has been no point, at any time in Hong Kong's history, where any government British or Chinese has given the slightest fuck about Hong Kong's democratic rights. I find it easier to believe that the British army can deploy a force of Action Men who can hold off the Red Army by a margin of a hundred to one than that any government that is even a vaguely plausible force in London would suddenly care about the people of Hong Kong.
I love that city. The family I have there love it. But it's only ever been worth anything to its rulers as trading floor.