Absolutely ! This thread is about natural rivers and the long term state of them (and on a non magical earth like planet too). Post flood and tsunami... well almost anything goes. Then in the medium time span there is this braiding and some extreme cases of meandering then longer still you might have oddities from glaciers periodically freezing and thawing in multi decade cycles but generally, in the long term, the idea that rivers don't fork and exit into the sea in one spot holds true. I guess if considered long enough then any river system is dynamic enough that there is no stable state for it but for the maps we make here that's not really applicable.