There are several possible Chinese goals here, none of which require permanently closed borders:
1. Zero Covid until mRNA vaccines become available to them. Given the infectivity of Omicron and the technical hurdles to mRNA vaccines, they seem unlikely to succeed here.
2. Contain the burn to one city/region at a time so that resources from across the country can be moved in, reducing deaths. Again, seems unlikely to be possible given the infectivity of Omicron, but this goal requires quarantined borders to work.
3. Wait until less lethal variants arise, then select only less lethal variants to allow into the country. Given their failure in keeping out Delta and Omicron, this seems impossible, but it would be a good goal. It is complicated by their lack of effective vaccination, which makes comparing variants hard.
4. Continue Zero Covid as theater to avoid undermining the government's legitimacy, perhaps until the population can become quietly infected. This could be combined with ineffective testing, variant selection, and more effective censorship. (And perhaps border closures need only occur until these systems are in place.)
5. Maintain Zero Covid until the next political meeting. Let the floodgates loose after the current government is stable.
6. Find a way to end Zero Covid which can be blamed on political enemies (domestic or foreign).
Honestly, I am skeptical both that the Chinese have a real long term plan, and that their current border restrictions cannot be maintained forever. While it seems impossible to contain a virus with the infectivity of measles, it is travellers who pay for the border quarantines. The state might enjoy maintaining them merely as a way of reducing contact with subversive foreign ideas.