I'm a bit more pessimistic that short haul will bounce back sooner than long haul.
With only 11% of Europeans vaccinated (compared to 50% UK). Even the vaccine leading UK ,it will be August at the earliest before the UK will have vaccinated anything like the sufficient number of under 50s to enable relaxation. Even then, I can see a combo of testing & quarantine on arrival back to the UK. That won't make short European holiday trips viable for many.
On the other hand there is business & substantial family requirements for long haul that the inconvenience of testing/quarantine on arrival both ends is worthwhile. I can see CX, HU & SIA for instance re-introducing a limited schedule, along with the EI US routes. If the alleged Islamabad load factors mentioned above are true, that reinforces the family travel demand, despite quarantine rules.
This scenario is more realistic than expecting a return to multiple Alicante & Malaga's this side of October.
There is also the huge cargo demand from the longhaul services that would contribute to their viability.