I don't think there's any great secret about what we'd do, other than do anything to prevent the very worst.
I read the posting urging crew to chop intruder's heads off with the fire axe and in principle I agree that the rules have changed.
The old rule of 'co-operate' and 'take them where they want to go' don't apply any more but one must temper that by not inciting the pilots to butcher anyone that blunders in. That person may be drunk, under the influence of drugs or just plain mad and may be easily restrained without resorting to gouging their eyes out with a stolen hotel biro.
If push really came to shove, I'd opt to go for a forced landing or a ditching to stop the aircraft being used as a weapon, in the hope that a throttle idle, speedbrakes out max angle descent would keep the murderous b******s out for a bit longer.