I find that a piece-by-piece translation can often be detrimental, because it tends to ignore what you stated, the 'HOW'. In other words, certain elements in one language or another can be expressed by a single word/suffix, although it may not be as simply stated in the opposite language. Because of this, single example sentences are almost never sufficient; it usually helps to have many sentences so that you are able to stop focusing on strict translations, and focus more on trends that a particular element enforces on meaning of the sentence. *especially* with JLPT material, I often see 3 or 4 grammar structures that, if translated into an 'easy to understand' english definition, all appear to be the same. Likewise, the translations often focus more on a superficial understanding (as there is so much to memorize) than really digging into the nuances of the language.
As to the sentence you mentioned, it's the first time to see '危篤', but I'd say it translates to
"My friend caused a traffic accident and is in serious condition". The を is acting on the traffic accident, specifically, 'caused a traffic accident'. There is no 'special' form hidden in the grammar that suggests that it's causative, it's simply a foregone conclusion that because of the traffic accident, they are on the verge of death.
Although the more polite form of Japanese begs to differ, most natural Japanese does do as much as English does to simply, contract, and shorten speech. So, check out the sentence below.
My friend caused a car accident, beacuse of that they are in critical condition. / Because my friend caused a car accident, they are in bad shape.
*or*
My friend caused a car accident and they are in critical condition.
I would argue that the second in more natural, easier to understand, and strips out unnecessary information that is understood from the context of the sentence.