Bitcoin will be worthless too if fiat is worthless and that's right since we're using fiat right now mainly. But what if the prices of everything are in bitcoin form instead? For example, a coffee is cost 0.0002BTC? Regardless if fiat has value or not, bitcoin would always have value. I think this is a possible scenario but it would take a lot of time before this happens. The majority of fiat have to be converted in bitcoins first. Basically, the whole thing should be upside down. This time, fiat depends on bitcoin.
I didn't quite understand what you meant to say on the whole, but if I got your point right, you basically claim that without fiat Bitcoin would be worthless too. This is an old story which people tend to repeat regularly. Nevertheless, if everything is priced in Bitcoin directly, wouldn't that prove the contrary? That is, that Bitcoin has value since you can pay with it for a cup of coffee (leaving aside technical issues)? There are no existential barriers to price anything priceable directly in bitcoins (I repeat it again for dumbasses that I discard technical issues), and we don't need to convert any fiat to bitcoin at that...
Since all paper will burn in the end
I think I kind of messed up at the part where I put it on bold (the one in the black font) so you kind of got confused to what I was trying to say. Try reading without the green highlighted part. We were basically saying the same thing.. If this whole currency dependency was turned upside down, fiat being worthless wouldn't mean anything to us (I might be repeating myself but whatever...) because at that time, bitcoin would be the standard measure of all currencies both crypto or fiat.
At that point, if all papers were burned, bitcoiners would all be like "Meh. Just like what I expected back when bitcoins wasn't yet popular."