WI... the Hong Kong New Territories lease was perpetual?

This makes no permanent difference; China could take Hong Kong whenever it wanted to enough.

However, in OTL, the end of the lease provided a plausible date and reason for the handover. China felt no need to press the issue, because they would get it eventually.

If there is no such scheduled end date, what happens instead?

(How early was this a factor in Chinese thinking? One could imagine Mao thinking that since the war with the KMT was won, the imperialist toeholds should now be dealt with. But China actually did nothing then, out of prudence. By the 1960s or 1970s, China would be more confident, but still did not act. Was the future end of the lease already a consideration?)
After the Japanese defeat in the Second World War, Hong Kong gets handed over to China, because Jiang will demand it - and if he doesn't succeed, Mao will. Hong Kong and Taiwan were Jiang's two main red lines for reconquering lost Chinese territory (HK even more so because of its symbolic value to the GMD's history), and on top of that was the end of all foreign concessions (which HK basically was). Perpetual occupations/leases meant nothing to the GMD in this case.
True, but theres also the liekly hood of Honk Kong becoming another Taiwain. Supported by the West against China.
True, but theres also the liekly hood of Honk Kong becoming another Taiwain. Supported by the West against China.
Not really, no. By the end of WWII, even Britain wanted to eventually get out of HK as it no longer had any use (Churchill's rumblings can be discounted here, as he increasingly became unrepresentative of what was actually happening in Britain). In addition, Taiwan is a specific case that does not really apply to HK. Not too many people would be willing to support continued colonialism in China, and the expectation after WWII was that HK would fall under Chinese jurisdiction. Even if the Warlord Period went in a different direction, or still continued, ultimately HK will get drawn in and fall under *a* Chinese government at some point. It also helps that Hong Kongers were, by and large, Chinese nationalists, which was unlike the case in Taiwan where things were a lot more complicated.
Macau--where the Portuguese *did* have "perpetual" right of occupation-- offers an interesting comparison. (From the 1887 Sino-Portuguese Treaty of Peking: "China confirms, in its entirety, the second Article of the Protocol of Lisbon, relating to the perpetual occupation and government of Macao by Portugal." https://en.wikipedia.org/wiki/Sino-Portuguese_Treaty_of_Peking)

A post of mine from a couple of years ago:

"Yes, I know that after the Carnation Revolution, Portugal offered Macau to the PRC and the latter turned it down. But the fact remains that China could have had Macau back whenever she wanted it. For a long time she didn't want it because the lifeblood of Macau was gambling, and the PRC would have been embarrassed to allow casinos on her territory--yet to crack down on gambling and organized crime in Macau would have been financially ruinous, "killing the goose that laid the golden egg." Once you got a PRC government wiling to tolerate very un-Communist behavior in its "special administrative regions" the PRC would find some way to incorporate both Hong Kong and Macau, regardless of their legal status and regardless of whether the UK and Portugal wanted to part with them." https://www.alternatehistory.com/forum/threads/ahc-independent-hong-kong.480230/page-2#post-19942017