The predestination is imposed by a curse placed when the NP is invoked. If you overcome the lance's magical energy, it doesn't inflict the curse and you don't have to worry about it.
That's... not how you get past Gae Bolg's Casualty Strike at all...
"In that regard, Lancer's lance is appropriate to be called a Noble Phantasm.
A weapon that always strikes the heart cannot be blocked merely by knowing about it.
If one is to oppose that demonic lance, one must…
Prepare a shield overwhelming the magical energy of the lance,
have great enough luck to change the fate determined by the lance,
or prevent him from using the lance in the first place."
I know direct statements from F/SN are inconvenient for people's perception of Gae Bolg, but they still exist.
That statement literally contradicts your stance that "having enough energy can stop The Casualty Strike" because it literally says "Prepare a Shield"! Nasu very clearly means something like Rho Aias, I have no idea how you think this means anything when any major Heroic Spirit can casually tank it when we see from Fate/Extella and Jeanne D'Arc, it is not enough!
Siriel, stop fucking lying!
Because people don't like discussing about Emiya fighting like he does in canon and prefer talking about offscreen stuff that he never does.
Yeah, ignore the times where EMIYA uses Gae Bolg in canon... like Unlimited Codes... and the Extella series... and F/SN itself... or the fact in FGO, he states he can project Gae Bolg...
Seriously, EMIYA kills the dweeb like nothing and it's only the wankers and downplayers who pretend EMIYA REALLY has to dig deep to kill Yuta.
EDIT: This is also hilarious this is coming from Siriel, who has been shown on countless occassions to blatantly lie about the Nasuverse and the Events in it for his own reasons.