I wonder if using English letters to write Russian phrases is acceptable practice for native Russians.
Does it sound respectful, neutral or like a mockery?
I don't mean in context of that post, which obviously is respectful, but in general. Especially when unicode is a thing and you could just write до свидания
Flip note: the letters are not 'English', they are Latin (or Roman).
Back on topic, as a speaker of another language using Cyrillic, for me romanisation is perfectly normal/expected in this context. I don't expect English speakers to have to learn a new alphabet just to be able to read the title of a blog post which is otherwise in English.
Back when texting (SMS) was still a big thing, you had a choice to either write in English letters and enjoy 140 char limit per message or write in Cyrillic and have it reduced to 70 chars. Many were doing the former. I assume many other countries with non-latin alphabet had the same.