The successor will be Barnaby Joice (sic).
Successor in the portfolio or as leader of the Nats? If you mean the latter I have heard (from a mates second cousin whose best friend is going out with a girl whose father works with someone whose brother is in parliament) that Truss is hanging on until a suitable successor, other than Joyce, can be found.
As to unsaddling regional aviation costs, well, thats just about the funniest thing you will read this year, or any other year. The minister has nothing to do with it, in fact the minister has nothing to do with aviation full stop.
Nothing will change until CASA is totally rebuilt from the top down. There has to be a root and branch clean out with a clear policy direction in line with the NZ approach and the necessary brawn to ensure compliance. Failing that the only hope is for someone like the FAA to review their audit of CASA and decide that nothing has changed and therefore it is a "fail".