Actually it won't. If she does not die in battle Mathilde could well outlive most dwarfs. So to the question of who will come after Mathilde the answer is 'a more experienced Mathilde'. Let's please not assume that spreading around shameful dwarf secrets will somehow make diplomacy better and he worth the risk of said secrets eventually getting into unfriendly hands
Actually, how long do wizards live? Human wizards, I mean. Because Dwarfs lives for centuries. Possibly millennia. Whereas the usual human wizard, even a powerful one, is probably lucky to live past a century.
Or are we functioning on, as chocolote12 put it, "Well, you see, it was mentioned once as a potential option, so we practically have it already" logic where "Well you see, it was mentioned that Gold Wizards turn themselves into Gold once, so therefore this means Golds have immortality for sure (rather than a rumor or assumption about it) and therefore
all wizards are expected to be immortal" "Lots of posters have talked about this Gold Wizard thing, over many years and many threads of warhammer fantasy, so it's practically accepted knowledge now."
==============
Also, I'm a bit concerned with the cavalier way teleportation is assumed. In an iron platform (so swimming in chamon) already heavily enchanted to fly. Windherder might allow it, but just doing fixed beacon-towers seems 20x as practical to me.
Well, you see, it was mentioned once as a potential option, so we practically have it already. No need to actually go and take all those research options or whatever, it'll just be ready when we need it.
==============
How many ageless human wizards do we actually
know?
Because I don't think that we know enough immortal-for-sure human wizards to say "Wizards are ageless by default."
Maybe you have
some wizards achieve agelessness or a form of immortality. But it is not something to be assumed.
Also? I would super not bet on Mathilde, specifically, living past a century. Because the way we currently act, we'll get ourselves killed within that century. Unless we retire from dangerous stuff, and be mainly a researcher, scholar, and Loremaster of K8P. So even
if wizards were ageless somehow, I would still not bet on
Mathilde specifically outliving a Dwarf.