Having removed dropouts for a repair... where you want to save the adjacent tubes...
It takes a surprising amount of heat, rosebud tip helps.
The trick is getting the whole joint hot to get enough of the brass (almost always brass) to flow again at the same time.

I should add that when I was taking things apart, the dropout was overheated as it was waste.

If you have a damaged frame that will not be rebuilt then you could with a hack saw and file get the job done.

You will have some joint material to mechanically clean up, both brass and silver "wet out" and fill the exterior grain of the steel.
That is what helped make the joint strong enough to begin with.

Beware of pins. You will be surprised how many frames have them one one or both of the stays.
So strip all the paint off first should you go with heat to harvest.