I have used a pinpoint flame
without causing any damage to the hydraulic lines and also saving the nut/flair fitting.
What DID get damaged is the flex hose extension, which is the main reason for removing it.
Cutting the flex hose first removes any danger of the hose bursting under pressure.
Damage to the brake fluid is a non-issue because it's got to be flushed out anyway.
I haven't really heard a valid reason for NOT using heat (heat being a pinpoint flame) to free up the flair nut.
As always, care should be taken. I've done it using pinpoint flame several times with no negative result.
Re-flaring that end can be a real P.I.T.A., and getting the proper flair nut to fit the line can also be the same.
But, if the flair nut is toast, (which it will be using vice grips) maybe cutting the line to
get it all out in the open is your best option. You've got choices.
Good luck!