Whats the deal with this. do you lose them if you die. Or just some of the progress or how does this work?

Deaths reflect negatively on all of your weapon and charm proficiences and will lose a percentage of your accumulated progress if you die. With crafting proficiencies, you are unable to lose any percentage for failing to complete a certain crafting task, or by death


http://ladderslasher.d2jsp.org/index.php?g=1

u loose x % of the current progress.
u can`t loose a prof lvl, so going down to 1 xp of prof on current lvl will be lowest u`ll fall.
i don`t know, if % of loss is determined by the number of mq passes u had on that char, like it is with xp, but i think % of profloss is on all classes same.

You lose them all only if die on hardcore.

Ok thanks fellas