I don't know if the billon dollar one will have that feature but this one does has solutions for that. If you click on preview, what you have written is saved, and if you accidentally click on the back arrow, then click on the forward arrow and the text is as it is.
I would expect the new forum to be like that or better.
In mobile phone using firefox browser won't erase or I don't have to type my post from the start. I didn't even uee preview and when I press back It is still there when I press forward. Honestly, I have been doing it since I joined this forum where I have to oress back to see the first page and then forward to continue typing my post. It my case, it won't be gone as long as I didn't press anything that will load or redirect because it will replace the data and when you try to press backward and then forward then it won't be the where you are typing your posts. Anyway, while I am typing this post I did use the backward or back arrow and then forward to see posts from the last page I visited.