It depends on what you mean by ‘accrued leave’. The company is on record that any leave currently in your leave bank retains full value. However it appears from reading between the lines on webinars that with a lower MGH, leave accrued in the future with a lower MGH will have a lower value.
Again, it’d have to be a massive quid pro quo to seriously consider this.
The quid pro quo will be "We're offering you additional chances to do some flying and earn at least half of your normal income." Whilst the number of pilots who benefit from that outnumber the pilots who will be relying to any degree on previously and future accrued leave for any Qantas income in the next few years, the vote will get up.