"My grandfather died yesterday."
お悔やみ(を)申し上げます okuyami-(wo)-mōshi-agemasu We would like to express our condolences.
お心遣いありがとうございます。 O kokorodzukai arigatōgozaimasu. Thank you for your sympathy.
Since gai-jin/ foreigners often go for work, it seems more likely one will be in a position to say the former. But to one's boss/ superior? Please, is it rude or not?This is confusing:
これもYahoo!知恵袋などの質問系サイトに良く載っている質問です。 もしかしたら目上の人から使う言葉ではないか、部下から使っても良いのか、という主旨のようです。 全く問題ありません。相手がどんな立場であれ、全く失礼の無い言葉です。
I challenge the use of 'g'in this sentence. I would use 'wa' because the point of the sentence is that he died. That is the news of it. Using 'ga' has the implication that the sentence means it was said with 'ga' to highlight grandfather in response to there being confusion over who died. But the sentence would be different to convey that anyway.
I feel the opposite: は is possible, but が sounds much more neutral to me. With an intransitive verb like 死にます, the subject is generally marked with が. Using は to my ear would create contrast, saying "it is my grandfather who died, rather than someone else", or it marks "my grandfather" as the topic: "speaking of my grandfather, he died."
See Learn Japanese Adventure: https://www.learn-japanese-adventure.com/japanese-verbs-transitive.html