Agreed, capex will have to increase quite a bit over the next decade. But, I'm not as concerned about that as some.
Qantas has paid back about $3b in debt over the past few years, giving it room to take on new debt if required. It has also bought out a number of leases, and paid cash for most (all?) of the new 787s, freeing up cashflow. It has regained an investment grade rating, and has gone to pains to demonstrate that it can produce strong returns for shareholders over time.
All of those things mean that Qantas has a range of options to finance, lease or tap shareholders to pay for its fleet, and can likely do so on reasonably favourable terms - it doesn't have to pay for all of it from cashflow.