The B-52's relatively low cost of operation/maintenance, its ease of integrating new payloads, are the other factors why they will remain in service after B-1s. B-52s remain low cost, large payload, standoff weapons carrying platforms.
Development of a "semi-stealthy Tu-22M" or development of a clean sheet semi-stealthy supersonic bomber will be time consuming and expensive, and will draw resources away from H-20. It most certainly cannot be done quickly. Even a Tu-22M3 project probably be more like 5-8 years than 2-3 years, and with dubious use.
If the PLA had to choose between a true VLO subsonic H-20 and a semi-stealthy supersonic bomber, they will choose H-20 every single day.
H-6K/J/N family aircraft will likely remain in PLA service for quite a long time (albeit likely in reduced number than now) for the same reason why B-52s remain in US service -- because of their relatively low operating cost, and the relative ease of integrating large payloads onto the aircraft. Each of H-6Ks six primary weapons pylons can carry 1.5 tons of ordnance. That's a lot of payload to work with.
And the ventral launch position on H-6N will be able to launch outsized weapons that H-20 likely cannot do.
I would also add that in a modern high intensity conflict, something like Tu-22M3 or B-1 is not that much more survivable than H-6K. Yes, being supersonic allows for superior ingress/egress of course, but the RCS of those aircraft are not sizeable and you would not be deploying such platforms against any sort of enemy that still has a meaningful CAP in place anymore than you would a H-6K or B-52.
All of those aircraft would be launching standoff weapons in a high intensity conflict anyhow.
Now, there have been rumours of a JH-XX, i.e.: a properly stealthy and superonic capable regional bomber, but it would have a payload quite smaller than B-1 and even Tu-22M3. However it is not known if the PLA has committed to such a project yet.
Either way, pursuing a supersonic bomber (either a clean sheet one, semi stealthy one, or a modernized Tu-22M3) is not a simple or short affair and would require substantial dedication of resources, and anything short of a truly stealthy supersonic bomber would not be very survivable in a modern conflict, while being quite costly as well.
A bomber fleet of H-20 supplemented by H-6K/J/Ns is perfectly reasonable and sensible going into the medium term.
