I would be very cautious about this. You'd have a tight window to get back into Hong Kong, and if anything delayed you, the fact you wouldn't have a valid visa would mean your 7-year PR clock would reset back to zero. Some considerations:
1. You have to look at whether the airline would let you board the flight to HK, not just whether HK would let you enter once you arrive. You're likely to be denied boarding if your visa runs out before the compulsory quarantine would end.
2. The airline check-in staff have to administer the covid rules of n x m jurisdictions, any of which can change without warning — ideally you don't want to be in a position where you're stood at the desk with the gate about to close, trying to convince them of some fairly complex details of how Hong Kong immigration law administers right of abode applications.
3. If you tested positive for Covid you'd be denied boarding.
4. If arrivals from the UK remained barred (as they currently are), it's unlikely you'd be able to return in time.
5. If the airline cancelled or rescheduled the flight due to Covid disruption, you might not be able to return in time.
6. I'm not 100% sure they'd allow your early VEPIC application if you left Hong Kong before your 7-year anniversary *and* you don't have a visa for the time beyond. That would mean there'd never been a moment where you were a HK resident physically present in Hong Kong who'd completed 7 years — which is the stated requirement for VEPIC approval.
If you really need to leave before your 7-year anniversary, you could maybe explore other means of getting a visa for the time beyond, so you're not so dependent on arriving back at an exact date. I'd strongly recommend seeking advice from https://hongkongvisageeza.com/ who can help you work out the most robust plan possible based on the details of your situation.