It is anticipated that armed helicopters deployed for frontline combat will be replaced by various types of unmanned aerial vehicles. Will this heavy-duty armed helicopter enter mass service in the future, or will it only undergo small-scale trial deployment?
The only thing that could effectively replace an attack helicopter is an unmanned drone of comparable range, with a comparable sensor suite and similar weapons payload. So basically an unmanned attack helicopter.
Yes countries like the US, South Korea or Japan seek to supplement their existing helicopter forces with UAVs and cut future procurements in favor of such systems. And while many point towards the war in Ukraine as an example of how "attack helicopters are done!", the very same war also proves how effective these helicopters can be if deployed differently. Russian helicopters like the Ka-52/Ka-52M and Mi-28/Mi-28NM have proven, that when deployed cautiously and more defensively, that they're able to inflict heavy casualties and stop opposing assaults. They didn't do that alone, but together with drones, infantry, artillery, fighter bombers and cleverly placed mine fields, but they have been vital assets. They were crucial in shattering the Ukrainian counter offensive and they have also heavily contributed to driving out the Ukrainians from Kursk. These instances had the helicopters operate under the cover of friendly air defense assets and being able to engage targets that were either entrenched our susceptible to attack by maneuvering. Their ability to loiter, respond quickly and carry significant amounts of ordnance and sensors with them makes them lethal platforms.
Europe isn't abandoning the attack helicopter either, with the AW249 Fenice on the horizon in Italy for example. And Russia is heavily invested to modernize their existing fleet and they're producing new helicopters as well. And IIRC there is a project for a next generation helicopter underway as well, or at least rumored to be. Because of that, I don't really see why China would give up on the concept of the attack helicopter, if anything they'll be able to make some serious money from exporting them to countries who can truly need such a capability. While China itself will see the value in certain theaters against certain adversaries. Makes me wonder how well the Z-21 will be suited to operating at high altitude in mountainous regions.