It'll be most likely that both Mr Frogs will be dead by the time of SBII from old age, but naming childrens after historical figures is a common occurrence in dwarf culture, as Syrupleaf showed.
As to the fearless ness we'll have at least two, possibly more castes that will face our enemies with dignity and not a shred of apparent fear. If said lack of fear is courage or stupidity however will be anyone's guess.
Mr Frog has been shown to appear in Spearbreakers time and the future, even if we actually see/write him as dead there would be the possibility of him arriving somewhere in the middle of his ?time continuity?, at a point in time before he died.
Actually, the same applies to a sizeable portion of the Spearbreakers cast- Reudh, Urist, Vanya, etc.
There's two Mr Frog though, and both were probably about middle aged for their breed of gnome (since one was an almost exact copy, just with some semblance of empathy and morality regained over time by living amongst noncorporate dorfs, with soldiers who fight to protect others, not company interests and dorfs who work together for the common good of the fortress, more or less anyway.
Clone got left in the past, while actual Mr Frog is in the future/present, hence him being in two places. Everyone else meanwhile is either in one place or another, not both.
SBII willa ssume numerous history changes happen due to all sides saying fuck it and blasting the fuck out of eachother in the past, Joseph eventually being left in a place that he can't escape/dying and Eris mostly being demolished or so damaged it can never function as a real threat again, and a whole host of other things.