Detecting

Is the a way to detect when a unit misses during an attack or does a Critical Strike?

There is no event that would directly detect that. You can trigger the whole abilities, but that's a bit unreliable and/or CPU unfriendly and not so simple.

Maybe you should try to compare the life loss to the damage of the unit, even if it would be complicated and unrealiable.

So even starts the effect of ability can't catch passive abilities like that? I remember having problems detecting charge gold and lumber, for some reason it doesn't trip when "begins casting an ability".

you can do this but it is a bit hard, there are numerous posts on it so just search the forums for "deceting critical strike"