It's not a matter of preparing to prevent their death, but of simply being tough because they have a high Fortitude save, which is helpful against all sorts of dangerous magical supernatural effects, not to mention disease, poison, exhaustion, etc.
A 6th level Dragon Vassal Fighter has a base Fortitude save of +5.
With the +6 Constitution from the template and a +2 Constitution boosting item (only 400 IM and already standard issue among our baby adventurers) they should have a Constitution attribute of at least 22. That's another +6 bonus to their Fortitude save.
The template adds another +2 bonus to all saves, Fortitude included.
And an item with a +2 Resistance bonus only costs 400 IM and would likely be standard issue for our super-soldiers.
That's a constant Fortitude save bonus of +15, which could be further modified by gaining additional levels, another +2 from the Great Fortitude feat, and so on.
Basically, going lower than DC 25 would be trivializing the side-effect a bit too much to call it a side-effect.